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## Troubling Doubling at School

Math brain teasers require computations to solve.

 Puzzle ID: #49613 Fun: (2.89) Difficulty: (1.65) Category: Math Submitted By: dalfamnest

The number of girls who do wear a watch
is double the number who don't.
But the number of boys who do not wear a watch
is double the number who do.

If I tell you the number of girls in my class
is double the number of boys,
Can you tell me the number I teach? Here's a clue:
More than 20; below 32!

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 kittygirl19 Sep 27, 2012 First! Marple Oct 02, 2012 Second! RRAMMOHAN Oct 07, 2012 A bit tricky, but got it! Nice and simple explanation for the solution. Babe Dec 20, 2012 Fourth! I do not even tempt to figure these out. Not good at math, plus it is not myfavorite to do! Sorry! jaycr Dec 20, 2012 Hmm, this could be interesting... HABS2933 Dec 20, 2012 Fairly easy, but still fun. Though not for everyone, I do enjoy math (and most other subjects for that matter). HABS2933 Dec 20, 2012 Fairly easy, but still fun. Though not for everyone, I do enjoy math (and most other subjects for that matter). iggy39 Dec 20, 2012 Me too Babe, I don't have the brain to work these out. dsjt Dec 21, 2012 dalfamnest, can you please explain how you know that the boys must be a multiple of three so that those of us who did not find it obvious can learn? dalfamnest Jan 06, 2013 Hi dsjt...and others. Because the number who 'do' is double the number who 'don't', there must be TWO who 'do' for every ONE who 'doesn't'. So you could arrange them in groups of THREE - 2 who 'do' with 1 who 'doesn't'. The total number must therefore be a multiple of THREE. I hope that helps - sorry for the delay replying ... I've had a holiday! Happy New Year to all - keep enjoying this site! Jimbo Dec 07, 2014 Good teaser. Nice to see logical solutions that do not necessarily have to resort to algebra. ron93 May 05, 2015 Clever solution Eminem Jul 05, 2015 27 Its quite easy. Thanks to your clue i got tbe answer quickly Total girls = 3x Total boys= 6x (since there are double the girls) => 3x+6x=y => x= y/9 Possible solution is 27. catmom Dec 20, 2015 Once again I am reminded that math is NOT my strong suit. ultimatecub Dec 20, 2015 Nice one, I got it straight away. Only cube number of 3 in that range is 27