Question 725572
Solution:

Let 'x' be the sum of ages of 7 children.
Average age of 7 = x/7 = 12 or x = 84

When the avg age of 7 is 12years, a 6 year old child is lost.

That is (84 - 6) is the sum of the ages of 6 children.

Average age of 6 children = (84-6)/6 = 78/6 = 13 years