Question 145344
If the average age of the two Jones children is 5, then the sum of their ages must be 10, because the average of two values is computed by {{{AVG=(x[1]+x[2])/2}}}.  Likewise the sum of the 3 Smith childrens' ages must be {{{3*15=45}}}.  That means the sum of all 5 childrens' ages must be {{{10+45=55}}}, and the average of the 5 is {{{55/5=11}}}