Let P's age at the time of marriage be x . P's current age =x+15 According to the problem, x+15=8∕5×x Current age of P's son =1∕5×(x+15) Calculation: Let P's age at the time of marriage be x . Current age of P=x+15 x+15=8∕5×x ⇒x+15=8x∕5 ⇒5(x+15)=8x ⇒5x+75=8x ⇒75=8x−5x ⇒75=3x ⇒x=75∕3=25 P's current age =25+15=40 Current age of P's son =1∕5×40=8 Age of P's son 4 years ago =8−4=4 Age of P at that time (4 years ago) =40−4=36 Fraction of P's age =4∕36=1∕9