From Cartalk.

Dividing Time

RAY: Draw a clock face on a piece of paper. Using Arabic numerals put the appropriate numbers at 12, 1, 2, 3 and so on.Now, somewhere on the clock face, draft two lines. In doing so, you’re going to divide the clock face into segments, which contain numbers.

TOM: Do the lines have to go from one edge of the clock face to another?

RAY: Yes. So, when you draw the lines, you will wind up with either three or four segments of clock face. If the lines intersect someplace, you will wind up with four sections. If they don’t intersect, you will wind up with three sections.

The question is: Where do you draw the lines so that the sum of the numbers in each section is equal?

This one should get your students watching the clock that much closer.

I think I might use that one to start my 9th grade class on Tuesday. Thanks for posting the puzzle.

I got it! Spoiler ahead!

The groups are: (11,12,1,2) (10,9,3,4) (8,7,6,5)

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