A man wants to invest total Rs. 3900 in account of his two sons who are 14 years and 16 years old in such a way that they will get equal amount at the time of attaining the age of 18 years. If rate of interest per annum is 10% then find the amount he has to deposits in account of his younger son.

Rs. 1800

Let the share of younger and elder son is P₁ and P₂ respectively.

Time for younger son = 18 - 14 = 4 years

Time for elder son = 18 - 16 = 2 years

effective R% for younger son = 4 × 10 = 40%

effective R% for elder son = 2 × 10 = 20%

ATQ,

P₁ × \(\frac{140}{100}\) = P₂ × \(\frac{120}{100}\)

\(\frac{P_1}{P_2}\) = \(\frac{6}{7}\)

     P₁      :      P₂ 

      6       :       7    =    13

      ↓                            ↓

    ×300                      ×300

      ↓                            ↓

   1800                        3900