Let the present ages of A, B, F and S be ‘a’, ‘b’, ‘c’ and ‘d’ respectively.

Given, A is elder to B by 2 years

⇒ a = b + 2 -------- (1)

A’s father F is twice as old as A and B is twice as old as his sister S

⇒ c = 2a and b = 2d ------- (2)

Also, the ages of the father and sister differ by 40 years.

⇒ c – d = 40 ------- (3)

⇒ 2a – b/2 = 40

⇒ 2a – a/2 – 1 = 40

⇒ 3a/2 = 39

⇒ a = 26