20-6=14=remaining
since average of the 6 children is 5 years
that means (6childrenagessum)/6=5
times 6 both sides
6childrenagessum=30
the remainig chilren is 14 kids, of 8 average
that means (14childrenagessum)/14=8
times 14 both sides
14childrenagessum=112
so tht toal is 30+112=142=ttoal age of kids in library
20 kids so average age is 142/20=7.1 years average
