What number should replace the ? enter image description here

  • $\begingroup$ For the answer to be correct you need the 21 to be 20 $\endgroup$
    – Moti
    Commented Mar 1, 2015 at 3:42
  • $\begingroup$ I expected such a comment. If 21 was 20 then this would be a different puzzle. $\endgroup$ Commented Mar 1, 2015 at 3:49
  • $\begingroup$ So, the answer is not 15? $\endgroup$
    – Moti
    Commented Mar 1, 2015 at 4:40
  • $\begingroup$ No, it's not 15. $\endgroup$ Commented Mar 1, 2015 at 4:43
  • $\begingroup$ This puzzle was made by Nob Yoshihagara! I'm not sure what the policy on putting this in the post is, and I didn't want to edit for something this trivial. $\endgroup$
    – Deusovi
    Commented Jan 10, 2016 at 22:48

1 Answer 1


12 - (sum of digits) Well I don't like to spoil it entirely for others but here you go(since a moderator asked me to explain more): Add the digits of the two numbers in the circles that branch from a circle just one level above and place the sum in the circle. Eg. Start with 72 and 99 at the bottom, 7+2+9+9=27; put 27 up in there and so on...

And it did tease my brain a little. Thanks ;)

  • 1
    $\begingroup$ Thanks @Len . Added more explanation to the spoiler. I just didn't want to spoil it for the curious ones that can't help hover over spoilers while they're just looking for a hint. :) $\endgroup$
    – Donbhupi
    Commented Mar 1, 2015 at 5:11

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