Working backward to solve problems – Maurice Ashley

Translator: Andrea McDonough
Reviewer: Bedirhan Cinar There’s a myth
that grandmasters can see ten, fifteen, twenty moves ahead. And it’s a great myth
because I’m a grandmaster and it makes me look
like a super freaking genius. But the truth is, in just the first four moves, there are 318 billion ways you could play. Now, that would be cool
if I could pull that off, but grandmasters just can’t,
it’s too much. So we use different techniques
to be able to look ahead. And some of these techniques
include chunking, which means taking a group,
a chess position, and seeing what possibilities
can come from just that group; or pattern recognition, which is just going over a lot
of positions that look very similarly and extrapolating truths from that; the stepping-stone method, which is to take a position,
freeze it in your mind, and go from there
to guess the next position. But one of my favorites that I love to solve
these kind of chess puzzles, is called retrograde analysis. And what you do with retrograde analysis is that in order to look ahead,
it pays to look backwards. Now, why is this so useful? Well, in chess,
it’s a very complicated case. You got all these chess pieces,
it’s 32 pieces, but after five moves, the position
starts to evolve a little bit. And the game starts to go on and you see the chess position
get a little simpler, and a little bit simpler,
and less pieces on the board, until finally — in this case, a game that I played
in a tournament in Foxwoods, it gets to something like this. When great players play,
it often gets to something like this. You don’t see some easy, early checkmate. Grandmasters see through all that stuff. What you see is some end game,
something really, really simple. And we like to study things like this, grandmasters do, so that if we get to them,
we know how to play them cold, but also so that we can steer
the position that’s in front of us, the more complex ones you saw earlier, to something this easy, something this simple. So in this way, when you’re dead, I already knew like ten moves ago, because I knew where we were going. Now, why is this so effective? Well, it’s something about the human mind,
the problem with the human mind. We’re very logical creatures. So I want you to play along
with me a few games. Take a look at this sentence. [After reading this sentence, you will realize that the brain
doesn’t recognize a second “the.”] Now, most of you reading the sentence
the second time around will realize that you missed
the word “the” the first time around. Your mind is very logical,
it proceeds forward, it just ignores anything
that breaks with its logical stream, and so you don’t see
the word “the” the first time, the second “the,”
the first time you read it. But if you read this sentence backwards,
you would automatically catch it. You’d go backwards,
and you get to “brain,” you get to “the,” and then you say, “Whoa,
there are two ‘the’s’ in the sentence.” This is a really cool trick
for proofreading papers. You’re writing your paper
and there are these silly mistakes. Why are these mistakes in my paper? You read it backwards,
you’ll catch all of them. Alright, let’s go on to this problem,
an interesting problem. “Bacteria that double every 24 hours fill a lake it has infested
after precisely 60 days. On what day was the lake half-full?” Now, a lot of people see this problem and they’d think, “30, like,
you know, you split it in half.” Well, that’s not the right answer. And also people might want a calculator. It’s too big, it’s math, it’s boring,
I don’t want to do that either. But if you do this problem backwards,
you get the answer right away. What’s the answer? 59, obviously. You start at the end, you go backwards, it’s like, “Oh yeah,
it’s half-full, the answer is 59.” Here’s another puzzle,
a little bit more complicated. You have six numbers, 1 through 6. The cards are face down. You and I are going to pick a card. You pick a card and you look at it
and it says the number 2. I look at my card,
I think about it for a minute and I say, “I want to trade.” The reason I want to trade, we’re going to trade to see
who has the highest number at the end. Do you trade with me? Most people say,
“Of course, I got a 2, 2 sucks! There are four numbers higher,
probability says I’m going to do better.” Wrong answer,
you’re playing a grandmaster. You start from the back
and you work it out. If I had the number 6,
would I offer to trade? Of course not, I’m not dumb. What about the number 5? Probably not either, because you’re
not going to say yes if you have a 6. If 5 is not going to trade
and 6 is not going to trade, 4 is going to be like, “I’m not trading either,
because 5’s and 6’s don’t trade.” So you see what happens
as we work backwards. 3 is going to realize:
4, 5, and 6 — they don’t trade, so the offer is definitely a 1 and all of you who said yes,
thanks for your money. (Laughter) So, this retrograde analysis
is used in different places. It’s used to prove intoxications
hours after an alleged DUI by Pennsylvania police officers, which is kind of cool. Well, it means don’t drink and drive. The use of retro-analysis is used in law,
science, medicine, insurance, stock market, politics, career planning. But I find its use
to be in a more interesting place, maybe one of the most
interesting uses is in this movie, which I know a lot of you know, “The Curious Case of Benjamin Button,” where Brad Pitt plays a guy
who’s living his life backwards. And what this movie makes me
think of is that great quote, that quote you often hear
from people who are older, that youth is wasted on the young. Well, if you can see the end game, your youth will not be wasted on you. Thank you very much. (Applause)

100 thoughts on “Working backward to solve problems – Maurice Ashley”

  1. The card problem makes no sense. He has no reason to assume his opponent would think as logically as he does. He has to account for people who can't read numbers, who don't understand quantity, total morons, psychopaths. Most people would probably trade 1 2 or 3 and never trade 4 5 or 6. Some people will crazily offer to trade a 4 because they really want 5 or 6. To assume everyone is thinking as he does about ruling out 5 4 and 3 off then at in all trading scenarios, that's just a wrong evaluation. Not some deep creative epiphany

  2. If I read it backwards, word for word, I don't understand what I'm reading, how am I supposed to catch those small mistakes? Maybe he means read each sentence forward, but starting from the last sentence in a document?

  3. Actually he makes a lot of sense. Scientists commonly search for an answer that we know nothing about; but what if you pretend we found the answer and then do backward research on which methodology most likely caused the answer so that we can narrow down on the actual scientific goal. Thats how almost all inventions were made.

  4. Now I see the trick, all this time I have been thinking how is that possible grandmasters can calculate 15-20 moves ahead accurately.. Now I see they actually use the methods mentioned on the video.

    Now I am gonna do the same on my chess games, and guess what? Very soon I will the grandmaster too😊

  5. You know. It's funny I peaked at 2000 elo. With USCF…. (which is strong but nothing compared to a GM) I get that all the time from family or friends. "You must be a genius" its simple problem solving methods he uses and he happens to be better then the majority of humans. Somewhere along the line he has a gift or a intuition because I put in so much effort excel and I hit a plateu. I dont know how else to continue. To get to his level.

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  7. It's just like the bit in memory or the power of in math. It goes from 0, 1, 2, 4, 8, 16, 32, 64 … In day 59 it will be the half of what will be in day 60

  8. That example with the cards reminds me of the executioner paradox thing where the executioner says he'll execute a guy on a day of the week but the day will be a surprise so the prisoner thinks well it can't be Saturday because if it hadn't happened before then I would know it was on Saturday and I wouldn't be surprised and then because of that he thinks the same thing about Friday and then Wednesday and then Tuesday and then Monday and then Sunday and then he decides he can't do it on any day or it wouldn't be a surprise and then the executioner Killa him on a Thursday and the guy is suprised

  9. Even tho I read the sentence like everyone else my eye cought the word to be fuzzy. It was blurry and made me want to look back and readjust what was wrong but I already finished the sentence at this point.

  10. I inadvertently used this technique when doing those maze puzzles at school. Ya know – those draw the line the center of the maze ones. If you start from the middle it's so much easier and I dont know why

  11. Your logic for the 1-6 number problem is COMPLETELY wrong, and I'm surprised nobody else here has pointed out the flaw in your reasoning. There are cards numbered 1-6 and I draw 2, correct? And you say you want to trade. Okay.

    1) You wouldn't offer to trade if you had a 6 because it's the highest number.
    2) You wouldn't offer to trade if you had a 5 because it's more likely you'd end up with a lower number (1-4 versus only one higher, 6).
    3) You wouldn't offer to trade if you had a 4 because it's still likely you'd end up with a lower number (1-3 versus 5-6)
    4) You would only offer to trade if you were reasonable and got 1 or 3. In both cases, you're at a probabilistic advantage to trade.
    5) If I have a 2, I therefore have a 50% chance at getting the 3 and a 50% chance of getting the 1. I cannot guarantee a win.

  12. I wish I would have known this technique in College. I would have gotten so many more Girls. (Start with the EndGame)

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