### Brain Teasers

# Troubling Doubling at School

Math
Math brain teasers require computations to solve.

Read the little poem and answer its question if you can.

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!

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!

### Hint

The sum of number plus its double must be a multiple of 3.### Answer

27Solution:

The number of boys must be a multiple of 3 (3, 6, 9...) so that it can be split in the ratio of 2:1 (no watch:watch).

The number of girls is double the no. of boys (6, 12, 18...)

So the totals can only be 9, 18, 27...

Hide Hint Show Hint Hide Answer Show Answer

## What Next?

**Solve a Similar Brain Teaser...**

Or, get a random brain teaser.

If you become a registered user you can vote on this brain teaser, keep track of

which ones you have seen, and even make your own.

## Follow Braingle!