Let the age of father be x years and sum of the ages of his 4 children be y years. ⇒x=y . . . (i) After 10 years, father's age =x+10 and sum of ages of 4 children =y+40 and sum of ages of 4 children =y+40 According to the question, y+40=1.6(x+10) ⇒x+40=1.6(x+10)( from Eq. (i)) ⇒x+40=1.6x+16 ⇒40−16=1.6x−x ⇒24=0.6x ⇒x=