One year ago, the ratio of Gaurav’s and Sachin’s age was 6 : 7 respectively. Four years hence, this ratio would become 7 : 8. How old is Sachin ?

\par Let Gaurav's and Sachin's ages one year ago be 6x and 7x years respectively.

\par Gaurav's age 4 years hence = (6x + 1) + 4 = (6x + 5) years

\par Sachin's age 4 years hence = (7x + 1) + 4 = (7x + 5) years

\frac{6x + 5}{7x + 5} = \frac{7}{8}

8(6x + 5) = 7(7x + 5)

48x + 40 = 49x + 35

x = 5

\par Hence Sachin's present age = (7x + 1) = 36 years