Lesson 7. The cross /meet technique.



hello here we are again the sudoko guy with guess what a brand new technique which is so good I tell you what this technique will help you find big numbers and small numbers and most important of all it will help you find what you missed you'll notice up on the top of there's funny little symbols don't worry about that I'll tell it about that later but have you ever been doing a puzzle and you get stuck so you leave it you go off come back later and you look at it and then you say oh he'll come I didn't see that before well this technique is going to help you find those things that you missed it's so easy to miss so let's do the puzzle here we go we'll do the horizontal blocks first let's take you the ones we have only one oh by the way I should have mentioned in this puzzle I'm going to do something a little different I'm going to deliberately miss out some things you're ready for that see if you can recognize them okay as I said there's only one one two is I'm the leaf three there's only one three four there's no fours fives there are two fives the top and the bottom so in this block it has to be in the middle so there it goes there sixes no sixes sevens oh here's a little technique I'm going to show you watch this in this block we don't have a seven we know from that seven did you cannot have a seven there and there because it's already spoken for in that row therefore the seven has to be up in one of these three cells if that's the case we look down okay let's take this cell here we look down up that's seven cancels that one out in this column that seven cancels this one out so therefore a seven must go there now we have two sevens we have a top and a bottom so we can work out where the 7s go across in this block well again we could have a seven seven seven but let's look down this seven means you can't have a seven there this seven means that the cancels out of seven here therefore the seven has to go there let's look at eights let me see now or we have all the eights top middle and bottom nines will the nines a very similar to the seventh let's look at this because the nine is there you can't have a nine in this block anywhere in here because it's spoken for because of that row already having a nine so therefore we know for a fact that a nine could go in here but you know what let's look down and one let me just before I put that in let's look down or this nine cancels out that cell so therefore this definitely becomes a nine now we've got two nines a top and a bottom we can work out what should go in here let's have a look if a nine was there but there's no nine there so that would be a little nine and here there's no nine so that becomes a little nine so that that's a really neat little technique to watch for let's look at H we've got all the eights we did the nines now we'll go to these three horizontal blocks there's no ones that there is two there are two twos there's a two on the bottom there's a two on the top this block doesn't have it too but we know it has to be in the middle because we've got two filled up here so it can't be there because of that too so they can be in those two cells I don't see a two there or two there so we can put it there there's only one three four there's two fours there's a four here there's a four here this means a four could go over here and I look down here and look up and down here look up and down here no four so we can put a little four in each one which you can do if it's within a lot of line within a block remember what we did in a previous lesson okay let's push on now five there's only one five sixes there's no 6s 7s there are two 7s as a bottom and a top so over here in this empty block we could have a seven here or we could have a seven there very good eight there's only one eight nine there's only one nine let's now go to these three horizontal blocks ones there's only one one twos there's only one two threes there's only one three four there's no fours fives there's only one five sixes there's only one six seven how we finally got somewhere there's two sevens at the bottom in the middle so therefore we know a seven has to be over here so it cannot be in this one because of that seven so it has to be over here which will cancel that out but I'll come back to that in a minute eights there's only one eight nine we've got them all so let's boot due to the blocks here on the the vertical blocks once there's only one one twos there's a left a center and a right they're done great three is only one three four there's no force really big force that is five there's only one five six there's no six seven so we've got them all on a center right and left eight we're going to got one eight and nine we've only got one nine let's go to these vertical blocks once well here's an interesting little technique have a look at this this one means that in this block here you can't have a one there because it's already spoken for in that column but you could have a one here and here and because you can put it in two cells in a block then bio can be hit by me all means go ahead two's well there's only one two threes there's only one three four there's only one four fives and you miss them out sixes there's only one six 7s they are all there left center and right H there's two eights is the left and a right so in this block it has to be in the centre which means it has to be down in here and here well that's that's helpful nines well we have a right a left and a centre so all the lines are done now let's go over to these three vertical blocks ones no one's twos is only one two three only one three four only one four five there's two fives there's a five here up on the left there's a five in the centre so in this block it has to be on the right has to be there and there well now I can raise that seven because it's already there so we put a little five in there and a little five in there because when I look along here there's no fives gosh look at this there's a whole row that doesn't even have a number on it bit big number that is sixes there's no sixes sevens yes there's two seventh is this one and this one therefore this one becomes a seven and some of you may say well I saw that ahead of you if that's the case that's great eights where you have two eights one on the right one on the left in here we'll need to have an eight in the middle with a centre so we put an eight there and an eight there that'll that'll should help us somewhere along the way Nine's well we have two nines we have a nine here on the left and nine here in the center in this block it has to be on the right this section here but I see there's a nine here so that cancels that that cell so that makes this a nine and that a nine and then we have a matching pair very powerful well now folks we've now gone through the basic procedures we now look for rows columns and blocks that have only got one or two cells left and when I look at that I tell you I cannot find any so now what do we do well this is where we come to this next technique I want to teach you see all these symbols up here in each case we have a a vertical line in this case in case of this puzzle it's a it's a column and a horizontal line in this case it's a row that either cross each other or meet each other look at each one of these there all right angles and they all either cross each other or meet each other and so with that idea in mind let me show you how to do the cross meet system first of all we'll start at 9 and we'll work through two we'll start wining work through till nine so let's say we look for a block that doesn't have a 1 and I notice that this block doesn't have a 1 but we have a 1 over here and we have a 1 over here let's intersect or me have those cross each other and see what happens if I take this one and go up it will cancel that cell in that cell if I take this one and go this way it'll cancel that cell and that cell only two left of that one and that one for a 1 now I have to say a word of thanks here to one of my students who I was giving a private lesson her name was Erica wonderful lady she showed me what the pieces of paper and she would put these pieces of paper along the columns to help her find out the empty cells now we can't deal with paper on here so I'm using these pieces of cardboard just to show you what she did you may not need to do this but it's just another way of doing it here's the one down in here in this and so I'll put one there covering up our block without the one at whoops we'll try another one we'll try that one how's that and here is this one we'll cover that one up by doing this now we've covered up this block using that one and using this one to find out that there's two empty cells and we know by doing that that this is a 1 and that is a possible one so that's what she was doing using strips of paper to help her do this now I'm not saying you have to do that but if it helps you great now let's let's do another one here here's a one we can go one across here we can do a one down in here let's do that one I'll do this one here going straight down that column and here's that one that goes across so we'll do that one to that one as well is that better okay and this block doesn't have a one but you know a one could go there there and there if that's the case don't put any ones in because let me assure you that will lead to more confusion and it's much better to just put little numbers in to cells within a block so later on when you get to very advanced levels you could put in three but for the time being just limited to two if it goes if it can go in more than two let's leave it don't put anything in so let's go down to twos well here's two here so what you would do to do this put that across there and then she'd know okay let me let me do it this way she'd do this I just messed up and down there she put that to there she'd put a two here because this is crossing here she put that two there because there's a 2 underneath there then she would get and one more she had three pieces of paper and she would do this there's a two here so she'd cover that two up oh dear he's not sticking today oh dear anyway let me just hold him for you if there would be a two there and a two there now guess what in this block there's only one place for two and it's right there so that's what she was doing with her pieces of the paper you may be able to visually do it just as well some people have more difficulty by just looking up taking just two going up that cancels this one out I'll just correct this nine if I may and then should take this to this this two here that cancels this one out and you finish and they take this two and go that way cancel this one and you finish up with a real – now what are the ramifications of that let's have a look we have a two on the Left we have a two on the center so down in this block that doesn't have a – we'll need it – now we can go there or there but if I look over here there's a two so that cancels out that one so therefore this has to be a to excuse my funny – because I'm looking at it sideways now what's the ramification of that well and here's a two here there's a two there so in this block or two has to be on the top it can be there or there but if I look up here there's a two so that's where the two goes now what's the ramifications of that let's see if there is one yes there is we have a two on the left here we two in the center so in this block that doesn't have a – this becomes the – way to go well let's try and make that a bit neater shine that becomes a 2 well isn't that current tremendous once you get one number you get lots of other numbers using tmb and LCR let's go to 3s now okay let's hope the stick this time here's a three here and there's a three there so if we put a three and one down there and another one across here I'll put underneath three there what do we finish up with we finish up with only one place for a three to go there it is there so you can get rid of the eight and put the three in and which means that this becomes an eight okay that becomes an eight now let's look at the ramifications if there are any of that yes here's a three in the bottom there's a three in the middle this one doesn't have a three and it has to go up in here now what's the ramifications of that if any well this is in the center up here we've got one in the right so this block has to have along the left and that's the only place it can go great let's continue one we could we went that way and up but what about going up this way too let's see yes you can there's a three in the center there's a three in the left therefore this becomes a three on the right now that what's the ramification of that Chiqui this is neat here we have a three on the middle this is in the bottom therefore in this block we have to have a three up here which cancels out that one and therefore this becomes a one see the advantage of putting little numbers in just two cells now what does that do ramifications this with the three that three is on the left this three down here is on the right so this block has to have a three in the middle in the center and that three cancels out this one so this becomes a now that was incredible we went right around the whole puzzle-solving freeze I think we've got all threes now haven't we one two three four five six seven eight yeah nine okay we've got I think we've got all the three is fantastic now remember when we did this three this meet can be two one let's look at the ramifications of that while we're at it one one bottom middle this has to be a one now because of that one we can't have a one down on this column anyone's in this block have to be there so it becomes a one eight matching pair now because we know that one of these is going to be a 1 that means that this here right center that this has to be a 1 now any ramifications of that yes there is I've just noticed there's a 1 here and there's a 1 there therefore in this block that doesn't have a 1 it has to be they're all there let's look up oh there's a 1 up there so it can't be there has to be here well that's neat now because of that one what's the ramifications of that I just notice something that one and this one we have a left we have a right that has to be in the center well it's a 1 for sure okay it's a 1 for sure well it isn't that interesting we almost went right around the whole prism just doing ones oh because of that one guess what yes we can look at that oh I'm getting it all excited here's that one that makes this one an 8 therefore this becomes the real one okay now what's the ramification of that let me see we'll take the ones first one bottom Middle top well look here's a one that could be any of these three cells but can't be that one because of that one can't be that one because of this one it has to be this one so we've got a one there fantastic now that we do there's something we can do with the 8 – but I'll come back to that right now because I've seen something here yes a 6 you can go in there that's the only one left 1 2 3 4 or 5 yes it's a 6 we can finish it off very good all this has happened because we did a cross on the 3 amazing isn't it so it's getting much easier by doing that route now let's go to fours here's interesting there's only 4 here here here when they're all in one line of block a line of blocks it's not easy to do a cross but I have noticed something in this column there's no 4 I think is that right 1 2 3 there's no 4 so this will have to be a 4 now what does that do for 4 this becomes a 4 and 1 2 3 4 5 6 this becomes a 6 why that was neat so let's go to the fives now 5s we're going to cross with the fives and this was in one of those things that I missed and I want to show you the fantastic way in which they you can find mistakes or find not mistaken this is over finding what you missed here's a 5 here here's a 5 here if we put it over the top of if we put it over the top of this puzzle there's this block here there's only one left place left where it can go therefore you can put a 5 here in confidence so this has to be a 5 whoops I left it up there so this has to be a 5 now because that's a 5 let's look at the ramifications of both directions this is this middle that's the bottom this has to be there and while we knew that because there was only one left in that column and we could work it out by counting what was left in this block but there's more things to watch for this 5 means that we have two 5s in these columns here in these blocks here a 5 here and a 5 here what does that mean that means it can't be there it could be there or there that's a little extra thing to really really know well I touch the told you I'd get come back to the H didn't know okay middle top bottom this becomes a neat now let's probably what I can see an exit another number there too but I want to now go on to the sevens sevens we've got all the sevens I think one two three four five six seven eight we've got them all don't see any sevens missing anywhere and two three okay okay eight eight eight eight well if I did listen if I hadn't forgotten to do this eight here doing the cross method look what happens if I do an eight across here and I do an eight down here that helps me find an eight and I do an eight across there eight across their councils this one eight down here cancels this one eight eight and so we finish up that has the only place we can really put an eight so that's another way of checking now nine nines G where's now well one of the neat things about the cross meet system is that is that it helps you confirm that your little numbers are correct and I've just noticed there's a nine here and a nine here there's a nine here that goes up here as well that didn't help a lot but because there's a nine here that crosses out that nine because of the nine there with that more that's all filled up this nine means that that's the only to place a nine can go so that's good let's see what else other nines or here's another one if I take this nine and go across here and take that nine and go up well when this only come down it's all filled up that's the only place in nine can go so that helps you confirm numbers all the lines are there all the lines are there we've got most of the nines already now where this we done the cross meet system right from one to nine now what we do is that we look for rows columns and blocks that it only got one or two left in them and there's lots of them I can see for example up here oh gosh we've got lots of them where do I start well here again if so many different directions you can go when in these puzzles once you get to this stage for sure and what I do may be a bit different from you but if it works out great now in this block here we have a four and what's left one two three four and five six we're missing a 4 and a 6 and a 4 and a 6 matching pair we know there are matching pair because is I need two left but look here's a four here so that immediately changes the story so this is this becomes a 4 then this becomes a 6 now what are the ramifications of that well whoops no I did it wrong round the wrong way didn't I hurrying I've got to slow down here Robin slow down okay this becomes a 6 and that becomes a 4 because of that 4 there if that's a 4 and this is a 4 Center left down in here we network and put a 4 there now let's do the 6 we've put in the 6 didn't we okay well guess when this blocky there's only one left and it's a 1 2 people it's a 6 well that gives us now two 6s or 6 here and a 6 there therefore the 6 has to be there let me point out once again that when you get a matching pair no other number could go there some of my students have want to put a 6 6 6 but you can't put one there now because of that sex but that would put sixes all over the place over there you're only once those are there you know other numbers can go there okay well that that really got us somewhere now that's this is interesting if I go without six we've got lots of ramifications of all those things I did afford to begin with let's do the four four four this becomes a four which cancels out this 4 if that's the four therefore we could be in there and there and we done what there's a four up there if there's a foot here's a cross look at this cross cross there cross there the only place of four can go is there we'd like me to repeat that for you I know for a fact that that has to be four because here's a four that cancels out these two this 4 cancels out any one in this one so that has to be a four if this is a four and that's a four then one of these has to be a four well when we put that four in we didn't lose the ramifications in two ways and that's something that's easy to miss when you put a new number look in the ramifications going both directions and I did it down that way but it didn't do it this way but while I'm doing it this way this becomes a four and that would have helped us know what to do here too so because that's filled up let's see well now we're doing sixes this bottom middle the six can go there or there now what have we got left look this is very interesting if I look at this here over bought a six on the bottom of six at the top the six has to be here and here matching pair that's going to help because if I look at this column here there's only two cells left and we know that if there's only two cells left and that's a six nine this has to be a six nine – well that's interesting now and wolf boy this is so exciting there's so many things we can directions we could go so we know one of those can be five well look at this if that's the case because there was a five five there and there's a five here this has to be a five now that's interesting because when I look at that that means that this over here can't be a five it turns into a nine and this comes becomes a five let's see if that's a five nine five that nine cancels out this nine so that becomes a six this six cancelled out this one so that becomes a nine that cancels out this one so that becomes a six and that means we're getting very close now well let me see now what are we missing along this row one two three four five six seven eight it's an it's a nine right boy now we've only got one left in this column I wonder what it is to work it out one two three four five six seven it's an eight yes that would be correct because we can double check it by saying middle bottom and top and this block has only got one left and it is I think one well let's look at the six is one six six sixth yes I needed to check on the sixes and we can do it this way one two three four five six seven and I believe by using this new technique where you take a vertical and a horizontal and have a meet or cross you can get all kinds of extra big numbers and small numbers and pick up what used so that's it for today bye for now

44 thoughts on “Lesson 7. The cross /meet technique.”

  1. i am a beginner, just learning…I purchased a paperback of puzzles published by Telegraph Road #144….do I ever feel dumb….cannot finish what they call 'very easy'…and yet on the internet I have progressed to 'medium'…..total loss of confidence! What am I not getting? Are the internet puzzles super super easy peezy easy?

  2. I truly appreciate your methodical approach. I have learnt a lot from the process. The way you explain the procedures has helped me enjoy sudoku even more. Your are the best sudoku teacher. Thank you.

  3. instead of using all these different 'TECHNIQUES'  WITH EACH #, you can also just go thru each CELL one by one INSTEAD and put ALL the possible #'s in each cell, leaving out the #'s of course that are in the row, column or block of that cell…..its time consuming, but covers all the bases with one technique………once you have all the potential #'s in each cell you can start eliminating stuff

  4. Step 1. solve Col Six.

    Step 2. solve Col Four.

    Step 3. solve Row One.

    Step 4. solve Row Three.

    ###############################

    Col Six has 1,8,5,6,9.

    Leaving 2,3,4,7.

    The 7 has only one cell.

    Leaving 2,3,4.

    The 3/4 are in the middle block.

    Thus the 3/4 can't be in

    the middle block twice.

    The 2 has only one cell.

    Leaving 3,4.

    The 3 has only one cell.

    Leaving the 4 only one cell.

    ###############################

    Col Four has 8,2,3,9,7.

    Leaving 1,4,5,6.

    The 4/6 are in the center

    bottom block. Thus the

    5 & 1 need to be in

    rows 7 & 9 respectively.

    Leaving 4,6.

    The 4 has only one cell.

    Leaving the 6 only one cell.

    ###############################

    Row One has six cells filled.

    Leaving the need for 1,3,6.

    The 3 has only one cell.

    The 1 has only one cell.

    Leaving the 6 only one cell.

    ###############################

    Row Three needs 1,4,6,9.

    The 1,4,6 are in the upper

    center block solving 9.

    The 1 has to be at R3C1.

    The 4 has only one cell.

    Leaving the 6 only one cell.

    ###############################

    Row Seven has 9,1,5,6,8.

    Leaving the need for 2,3,4,7.

    The 2,3,7 are in the lower

    left block solving the 4.

    The 2,7 are in Col 8

    solving the 3.

    The 7 has only one cell.

    Leaving the 2 only one cell.

    ###############################

    Row Nine needs the 2,6,8.

    The 2 has only one cell.

    The 6 has only one cell.

    Leaving the 8 only one cell.

    ###############################

    Col Seven has 5,6,4,8,9.

    Leaving the need for 1,2,3,7.

    The 2 has only one cell.

    The 7 has only one cell.

    The 3 has only one cell.

    Leaving the 1 only one cell.

    ###############################

    Row Six has need of 1,6,8.

    Col One has a 1 & 6, solving 8.

    The 1 has only one cell.

    Leaving the 6 only one cell.

    ###############################

    Row Four has 3,7,8,4,2.

    Needing 1,5,6,9.

    Col One has 1,6,9. solving 5.

    Col Nine has 1,6. solving 9.

    The 1 has only one cell.

    Leaving the 6 only one cell.

    ###############################

    Col One needs 4 & 7

    The 7 has only one cell.

    Leaving the 4 only one cell.

    ###############################

    Col Nine needs 4 & 5

    The 5 has only one cell.

    Leaving the 4 only one cell.

    ###############################

    Col Three needs 6,8,9.

    It should be easy to find

    the correct cells.

    ###############################

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