The average of 80 boys in a class is 15. The average age of a group of 15 boys in the class is 16 and the average age of another 25 boys in the class is 14. What is the average age of the remaining boys in the class?

Required average
$$\eqalign{ & = \frac{{\left( {15 \times 80} \right) - \left[ {\left( {16 \times 15} \right) + \left( {14 \times 25} \right)} \right]}}{{80 - \left( {15 + 25} \right)}} \cr & = \frac{{1200 - \left( {240 + 350} \right)}}{{40}} \cr & = \frac{{610}}{{40}} \cr & = 15.25 \cr} $$