At present, ratio of age of mother to her daughter is 7 : 1.  After 5 years the ratio will be 4 : 1.  What is the difference (in years) in their present ages?

30

Mother     :     Daughter

   7           :          1      ←  (present time)

   4           :          1      ←  (after 5 years)

ATQ,

⇒ \(\frac{7R + 5}{1R + 5}\) = \(\frac{4}{1}\)

⇒ 7R + 5 = 4R + 20

⇒ 3R = 15

⇒ 1R = 5

Therefore, Difference of their present age = 7R - 1R = 6R = 6 × 5 = 30 years