The sum of ages of 5 children born at the intervals of 3 years each is 65 years. What is the age of the youngest child?

Question

A man had nine children, all born at regular intervals, and the sum of the squares of their ages was equal to the square of his own. What was the age of each? Every age was an exact number of years.

Answer 1

x+(x+3)+(x+6)+(x+9)+(x+12)=65 --> x=7 years old

Answer 2

X+(X+3)+(x+6)+(x+9)+(x+12)=65
5x+30=65
5x=65-30=35
X=35/5=7