Charlie is 40 years older than his daughter. 12 years from now, his daughter will be ¹₂ of his age while his son will be ³₅ of his daughter. Express his son’s present age as a fraction of Charlie's present age. Leave your answer in its simplest form.

	Charlie	Charlie's daughter	Charlie's son	Difference between Charlie and Charlie's daughter
Before	10 u - 12	5 u - 12	3 u - 12	40
Change	+ 12	+ 12	+ 12
After	2x5	1x5
		5x1	3x1
Comparing Charlie, his daughter and his son in the end	10 u	5 u	3 u	5 u

The repeated identity is the age of Charlie's daughter. LCM of 1 and 5 is 5.

The difference in age between Charlie and Charlie's daughter remains unchanged.

Difference in age between Charlie and Charlie's daughter
= 10 u - 5 u 
= 5 u 

5 u = 40

1 u = 40 ÷ 5 = 8

His son's present age 
= 3 u - 12
= 3 x 8 - 12
= 24 - 12
= 12

Charlie's present age
= 10 u - 12
= 10 x 8 - 12
= 80 - 12
= 68

His son's present age as a fraction of Charlie's present age
= ¹²₆₈
= ³₁₇

Answer(s): ³₁₇