10 years ago, a man’s age was 5 times of his son’s age. 2 years hence, twice his age will be equal to 4 times the age of his son. What is the present age (in years) of the son?

Correct option is D

Given:
Let the present age of man and his son be M years and S years respectively.
M- 10 = 5 (S -10) ………(i)
And
2(M+ 2) = 4 (S + 2) ………(ii)
Concept used:
Fundamental concept of ratio.
Solution :
M- 10 = 5 (S -10)
⇒ M- 10 =5S – 50
⇒ M = 5S – 50 +10
⇒ M =5S – 40 ………(iii)
And
2(M+ 2) = 4 (S + 2)
⇒ 2M + 4 =4S + 8
⇒ 2M = 4S + 8 – 4
⇒ 2M = 4S + 4
⇒ M = 2S +2……..(iv)
Now, equating (iii) and (iv),we get
5S – 40 =2S +2
⇒ 5S – 2S = 42
⇒ 3S = 42
⇒ S = 14
∴ the present age of son = 14 years.