Question

Daniel, my son, is exactly one fifth of my age. In 21 years time, I will be exactly twice his age. My wife is exactly seven times older than my daughter, Jessica. In 8 years time, my wife will be three times older than Jessica. How old is Daniel now?

Answer 1

Let Daniel's age be a
Ratio of age will be
Father : Daniel :: 5a: 1a
Thier total age will be 6a
Thier total age after 21 years = 6a + 21 -----1
Age ratio after 21 years =
Father : Daniel :: 2(a+21) : (a+21)
Thier total age = 3 (a+21) = 3a + 63. -------2
Now we have 1 = 2
6a + 21 = 3a + 63
a = 7 years is Daniels current age.

Answer 2

d: Daniel age now
a: my age now

5d=a
21 years later:
2(d+21)=a+21
2d+42=5d+21
3d=21
d=7

Daniel age is currently 7