Ten years ago A was half of B in age. If the ratio of their present ages is 3 : 4, what is the present age of A?

Question: Ten years ago A was half of B in age. If the ratio of their present ages is 3 : 4, what is the age present of A?

Solution:
Let, B's age 10 years ago = 2x years
and A's age 10 years ago = x years

Now,
A's age at present = (x + 10) years
B's age at present = (2x + 10) years

ATQ,
(x + 10) / (2x + 10) = 3/4
⇒ 4X + 40 = 6X + 30
⇒ 2x = 10
⇒ x = 5

∴ A's age at present = (5 + 10) = 15 years