The average age of 'a' boys is ‘b’ years and of ‘n’ girls ‘c’ years. The average age of all together is?
Choose the correct choice from the following answers:  A) (ab – nc)/ (a + n) years  B) (ab + nc)/ (a - n) years  C) (ab + nc)/ (a + n) years  D) (ab – nc)/ (a - n) years  E) None of these
(ab + nc) / (a+ n)   ANSWER:(ab + nc)/ (a + n) years
<result>C</result>
The average age of 'a' boys is ‘b’ years and of ‘n’ girls ‘c’ years. The average age of all together is?