Answer 1

It is given that the ratio of the ages of Sonu and Monu is 7: 5 . 
Let the present ages of Sonu and Monu be 7x and 5x years . 
After ten years: 
Age of Sonu = 7x + 10 years 
Age of Monu = 5x + 10 years
According to the question, 
\[\frac{7x + 10}{5x + 10} = \frac{9}{7}\]
or 49x + 70 = 45x + 90
or 49x - 45x = 90 - 70
or 4x = 20
or x = 5
∴ Present age of Sonu =\[ 7 \times 5 = 35\text{ years }. \]
 Present age of Monu =\[ 5 \times 5 = 25\text{ years }. \]