Question 787016
Average = sum/(# of numbers)<P>
For the six numbers, the problem gives (8+9+16 + (sum of other three))/6 = 12<P>
8+9+16= 33 and call the Sum of the other three numbers S.<P>
33 + S = 72<P>
S= 72-33=39<P>
Apply the average formula.  S is the sum of the three numbers, and there are 3.  S/3 = average.  39/3 = 13 is the average of the other three numbers.