Ratio between the present ages of A and B is 2 : 3, respectively. After 5 years, the ratio between their ages will be 3 : 4. What is B's age at present?

15 years

                           A  :  B

Present ages        2   :  3

After 5 years   2R+5  :  3R+5 = 3 : 4

⇒ \(\frac{2R+5}{3R+5}\) = \(\frac{3}{4}\)

⇒ 8R + 20 = 9R + 15

⇒          R  = 5

Present ages of A, B = 2 x 5, 3 x 5 = 10years, 15years