The sum of the present ages of a father and his son is 99 years. When the father was as old as his son is now, his age was four times to the age of his son at that time. The ratio of the present ages of the son and the father is.

4 : 7

Let the present age of son = x years , and the present age of father = y years 

ATQ, x + y = 99 years 

let n years ago ( where n is = y - x )  father's age is same as son's present age . then  father's age was four times to the age of his son at that time. 

4 ( x - n ) =( y - n ) 

4 ( x - y + x ) = ( y - y + x )

4x - 4y + 4x = x 

7x = 4 y 

\(\frac{x}{y}\) = \(\frac{4}{7}\)

   x  :  y 

   4  :  7