Question 954957
Let's call the youngest a. The next is therefore a+3. And the one after that a+6:
a+a+3+a+6+a+9+a+12+a+15 = 81 Add on the left
6a+45= 81 subtract 45 on both sides
6a= 36 divide both sides by 6:
a= 6 The youngest child is 6.
Proof:
6+(6+3)+(6+6)+(6+9)+(6+12)+(6+15)= 6+9+12+15+18+21= 81 Correct.