JAMB - Mathematics (1989 - No. 38)
In a family of 21 people, the average age is 14years. If the age of the grandfather is not counted, the average age drops to 12 years. What is the age of the grandfather?
35 years
40 years
42 years
54 years
Förklaring
Total age of the whole family = 21 x 14 = 294
Total age without the grandfather = 20 x 12 = 240
Age of grandfather = 294 - 240
= 54 years
Total age without the grandfather = 20 x 12 = 240
Age of grandfather = 294 - 240
= 54 years