The arithmetic mean of the ages of 30 pupils in a class is 15.3 years....

JAMB 1982

The arithmetic mean of the ages of 30 pupils in a class is 15.3 years. One boy leaves the class and one girl is enrolled, and the new average age of 30 pupils in the class becomes 15.2 years. How much older is the boy than the girl?

A. 30 years
B. 6 years
C. 9 years
D. 3 years
E. 1 year

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Correct Answer: Option D

Explanation

1st 30 pupils at average age of 15.3 yrs. give total age of 15.3 x 30 = 459yrs

2nd group of 30 pupils at average age of 15.2 yrs

give total age of 15.2 x 30 = 456yrs

Difference in age = 459 - 456

= 3 yrs

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