Math CentralQuandaries & Queries


Question from Kim, a parent:

I am trying to help my son with a bonus question on his homework assignment and I am stumped as to how to help him with this one.

Here it is:

Using a clock with a regular circular faced dial, draw two straight lines such that the sum of the numbers in each of the three areas is equal.

Your help would be greatly appreciated.


It's your son's bonus question, not yours. His teacher isn't interested in whether or not you can do it. We'll give you two hints but we strongly recommend that you support and encourage your son to solve the problem on his own.

  1. Add the numbers on the clock face and divide by 3 to see what the sum should be in each of the three areas.

  2. When adding 1 + 2 + ... + 11 + 12 in step 1 it is easiest to start at both ends and add towards the middle.
    1 + 12 = 13, 2 + 11 = 13, ...

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