The ratio between the present ages of A and B is 3 : 5.  If the ratio of their ages fives years hence becomes 13 : 20, then the present age of B is?

35

   A     :      B

   3     :      5      ←  (present time)

  13    :     20      ←  (after 5 years)

ATQ,

⇒ \(\frac{3x + 5}{5x + 5}\) = \(\frac{13}{20}\)

⇒ 60x + 100 = 65x + 65

⇒ 35 = 5x

⇒ x = 7

Therefore, Present age of B = 5x = 5 × 7 = 35 years