A woman divided $1 among 12 children. Boys got 7 cents; girls got 9 cents. How many girls were there?

We need 7b + 9g = 100, where b and g are whole numbers. Count by 7’s and see that 13 boys and 1 girl works, except that’s 14 children. Try a different combination: 8 x 9 + 4 x 7 works, and that’s 12 kids.

Or use an equation: 7b + 9(12 – b) = 100, which gives you b = 4 so g = 8.