Answer to the Friday Puzzle…..


coverOn Friday I posted this puzzle….

Can you move just one digit and make the following equation correct:

101 – 102 = 1

If you have not tried to solve it, have a go now.  For everyone else the answer is after the break….

Move the ‘2’ up half a line to make 101 – 102 = 1

Any other solutions?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.


39 comments on “Answer to the Friday Puzzle…..

  1. fotoflex2013 says:

    I thought it was similar to the matches puzzle:

  2. Paul Allen says:

    I got 101-102=1 turns into 101=102-1 by moving one of the lines in the equals sign. But to be fair he did say digits.

    • The Masked Twit says:

      It’s a bit weasley, but you could claim that the top bar of the equals sign is the digit “1” on its side.

    • Eddie says:

      I think it’s time you took off your mask to reveal the underlying twit.

    • ChrisR says:

      That was my solution that I didn’t think was the ‘correct’ one, except I used the bottom line of the equals sign, and pretended it was a match ‘1’. Stupidly after I’d commented on this on Friday I then re-read the comments and was hit by the spoiler

  3. Sri Lanka says:

    I too….

  4. safc4ever says:

    It doesn’t have to be Denary ie Base 10…

    In base 3, move the 2 to in front of the 1 on the right hand side:

    101 – 10 = 21 (Ten minus Three equals Seven)

    In case anyone is unfamiliar with number Bases, each digit to the left is n times the value of the digit to its right, with the right-most digit always being “One”, “n” is the Base number (Base n). in Base Ten, 10 is Ten and 100 is Ten x Ten (One Hundred) etc. In Base 3, 10 is Three and 100 is Tree x Three (Nine) etc.

  5. mgm75 says:

    Yes, I did get it right despite thinking the answer was a bit sneaky.

  6. beanfeast says:

    I got a different base-3 solution: 110-102=1

    In base-10 that is 12-11=1

  7. Jerry says:

    101 – 102 ≡ 1 without doing anything if you compute the answer in modulo 2 arithmetic. That is 101 ≡ 1 (mod 2), 102 ≡ 0 (mod2) , and 1 ≡ 1 (mod 2). Thus 101 – 102 ≡ 1 (mod 2). Math nerd? Yes, I suppose.

  8. Physicalist says:

    Nope, didn’t get it, despite some ten minutes of puzzling. I like it; good puzzle.

    (The matchstick solution did occur to me, but I’d have been disappointed if it were the correct answer given the term “digit”.)

  9. says:

    ҿֵѧⱾ飬ҲԸɵ飬ĿʼдʲôdzǸտİ档—————— ԭʼʼ ——————
    : “Richard Wiseman”
    ʱ: 2014310(һ) 4:31
    ռ: “1250493584”;
    : [New post] Answer to the Friday Puzzle..

    Richard Wiseman posted: “On Friday I posted this puzzle…. Can you move just one digit and make the following equation correct: 101 – 102 = 1 If you have not tried to solve it, have a go now. ?For everyone else the answer is after the break…. Move the ‘2’ up ha”

  10. Anonymous says:

    I had a different answer, but kinda like that. This was a good one.

  11. Julia says:

    I’d seen the puzzle before and still didn’t get it.

  12. Es genial… Muy interesante 😀

  13. Anonymous says:

    También, ¿puede ser?

  14. Anonymous says:

    Less than a minute

  15. Bill says:


  16. Alex b says:

    By moving my right index finger just so, I got

    1 = 1

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    It was helpful. Keep on posting!

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  22. 竹官 says:

    101-10^2=1 All you need is to move up the 2 of 102 a little bit to make 102 be 10^2.

  23. and what about this 65-43=21 move 2 number to make this equation true.?

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