When Risa was 41 years old, her daughter was 2 times her son's age. Risa would be twice her daughter's age when her son was 29 years old. How old would Risa be when her son was 10 years old?

	Risa	Daughter	Son
Before	41	2 u	1 u
Change	+ ?	+ ?	+ ?
After	2 p	1 p	29

The difference in the ages between Risa and her daughter remains unchanged.

Difference in Risa's and her daughter's ages at first
41 - 2 u = 2 p - 1 p
41 - 2 u = 1 p --- (1)

The difference in the ages between her daughter and her son remains unchanged.

Difference in her daughter's and her son's ages at first
2 u - 1 u = 1 p - 29
1 u + 29 = 1 p --- (2)

Make p the same.

(1) = (2)
41 - 2 u = 1 u + 29
1 u + 2 u = 41 - 29
3 u = 12

1 u = 12 ÷ 3 = 4

Age difference between Risa and her son
= 41 - 1 u
= 41 - 4
= 37

Risa's age when her son was 10 years old
= 37 + 10
= 47

Answer(s): 47