JAMB - Mathematics (1982 - No. 41)
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?
30 years
6 years
9 years
3 years
1 year
解释
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
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