Question 1101128
EXPLANATION:
An average of several values is the sum of those values divided by the number of values.
{{{average(couple)=sum(couple)/2}}} <---> {{{sum(couple)=2*average(couple)}}} .
So the sum of the man'd parents' ages is {{{2*70}}} ,
and the sum of ages of the man and his wife is {{{2*40}}} .
For the 3 children,
{{{average(children)=sum(children)/3}}}  <--->
 {{{sum(children)=3*average(children)}}} .
so the sum of the children's ages is {{{3*15}}}
When we add the ages of all {{{2+2+3=7}}} family members,
{{{sum(all)=sum(parents)+sum(man+wife)+sum(children)}}} .
 
So, the average we can calculate for the whole family is
{{{average=(2-70+2*40+3*15)/7=(140+80+45)/7=265/7=37&6/7="37.857142857142857142..."}}}