Question

Q7.

There are 15 children at a birthday party.
The mean age of the 15 children is 7 years.
9 of the 15 children are boys.
The mean age of the boys is 5 years.
Work out the mean age of the girls.

Answer 1

10

Explanation:

Let c = sum of ages of all children.

mean age of all children = c/15 = 7

c = 15 * 7 = 105

The sum of the ages of all children is 105.

Let b = sum of ages of the 9 boys.

mean age of boys = b/9 = 5

b = 9 * 5 = 45

The sum of the ages of the boys is 45.

The sum of the ages of the girls is c - b.

c - b = 105 - 45 = 60

The number of girls is 15 - 9 = 6

mean age of girls = (sum of ages of the girls)/(number of girls) =

= 60/6 = 10