Help a dumb guy out here. In Sunday’s “Ask Marilyn” column in Parade Magazine I read;

Here’s a puzzler: What does this set of equations describe?

1 + 2 = 3

3 + 4 = 7

5 + 6 = 11

7 + 8 = 3

9 + 10 = 7

11 + 11 = 10

Answer: The arithmetic of an ordinary 12-hour clock.

I don’t get it.