When Marion was 49 years old, her son was 2 times her daughter's age. Marion would be twice her son's age when her daughter was 37 years old. How old would Marion be when her daughter was 21 years old?

	Marion	Son	Daughter
Before	49	2 u	1 u
Change	+ ?	+ ?	+ ?
After	2 p	1 p	37

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

Difference in Marion's and her son's ages at first
49 - 2 u = 2 p - 1 p
49 - 2 u = 1 p --- (1)

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

Difference in her son's and her daughter's ages at first
2 u - 1 u = 1 p - 37
1 u + 37 = 1 p --- (2)

Make p the same.

(1) = (2)
49 - 2 u = 1 u + 37
1 u + 2 u = 49 - 37
3 u = 12

1 u = 12 ÷ 3 = 4

Age difference between Marion and her daughter
= 49 - 1 u
= 49 - 4
= 45

Marion's age when her daughter was 21 years old
= 45 + 21
= 66

Answer(s): 66