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Billy likes the number 25 but not 35. He likes 144 but not 145. He likes 8100 but not 8000.

Does he like 872 or 841?

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  • $\begingroup$ I edited the question and replaced "25 but not 25" with "25 but not 24" since it looked like a typo. Feel free to roll it back in case I did it wrong. $\endgroup$ – Marius Jun 6 '16 at 13:57
  • $\begingroup$ I actually put 25 but not 35. $\endgroup$ – Xxoplechic Jun 6 '16 at 18:11
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841

Because

he likes perfect squares.
$841 = 29^2$

he likes 25 because

$25 = 5^2$

He likes 144 because

$144 = 12^2$

He likes 8100 becasue

$8100 = 90^2$

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    $\begingroup$ This is only correct assuming the first line has a typo, and you probably shouldn't just edit someone's question like that $\endgroup$ – Gordon Allocman Jun 6 '16 at 13:50
  • $\begingroup$ @GordonAllocman it was a typo. I've seen this problem before. Here is one similar: free-iqtest.net/answers.asp?q=15 $\endgroup$ – Marius Jun 6 '16 at 13:51
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    $\begingroup$ This is a very well known puzzle. $\endgroup$ – Inazuma Jun 6 '16 at 13:53
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    $\begingroup$ Just because another similar question exists, doesn't mean it is exactly this one. While in all likelihood it was just a typo, you should really let OP fix it to be safe $\endgroup$ – Gordon Allocman Jun 6 '16 at 13:54
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    $\begingroup$ I agree. I guess I got an adrenaline rush because I knew the answer. I guess the OP can roll it back if there is a problem and earn a badge for "first rollback". $\endgroup$ – Marius Jun 6 '16 at 13:56
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That was easy. Billy likes

841.

Clearly because,

Billy likes perfect squares. 841 is the square of 29.

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