7 pupils of average age 12 years leave a class of 25 pupils of average age 14 years. If 6 new pupils of average age 11years join the class, what is the average age of the pupils now in the class?

A.
13years 
B.
12 years 7(frac{1}{2}) months 
C.
13 years 5 months 
D.
13 years 10 months 
E.
11 years
Correct Answer: Option D
Explanation
Total age of the 7 pupils = 7 x 12 = 84
Total age of the 25 pupils = 25 x 14 = 350
Total age of the 6 pupils = 6 x 11 = 66
7 pupils leaving a class of 25 pupils given 18 pupils
Total age of the 18 pupils = 350 – 84 = 266
6 pupils joining 18 pupils = 24
Total age of 24 pupils = 266 + 66 = 332
Average age of 24 pupils now in class (frac{332}{24})
= 13yrs 10 months