The ratio of ages of Mohan and Sohan is 3 : 4. Four years ago the ratio was 5 : 7. Find the present ages of Mohan and Sohan.

Let us assume the present ages of Mohan and Sohan be 3x years and 4x years; then,
4 Four years ago the ages was 3x - 4 and 4x - 4 years.
According to question, 4 Four years ago the ratio was 5 : 7
( 3x - 4 ) / ( 4x - 4 ) = 5/7
⇒ ( 3x - 4 ) 7 = 5 ( 4x - 4 )
⇒ 21x - 28 = 20x - 20
⇒ 21x - 20x = 28 - 20
∴ x = 8
Hence, their present ages, 3x = 3 x 8 = 24 years; 4x = 4 x 8 = 32 years.
So their present ages 24 and 32 years.