The average height of a group of girls was 129 cm. After 7 boys with a total of 973 cm joined the group, the average height of all the pupils increased to 131 cm.
- What was the average height of the boys?
- How many girls were there in the group?
|
Girls |
Boys |
Pupils |
Number |
1 u |
7 |
1 u + 7 |
Value |
129 |
? |
131 |
Total value |
129 u |
973 |
131 u + 917 |
(a)
Average height of boys
= 973 ÷ 7
= 139 cm
(b)
Total height of pupils
= 131(1 u + 7)
= 131 u + 917
Total height of girls and boys = 129 u + 973
131 u + 917 = 129 u + 973
131 u - 129 u = 973 - 917
2 u = 56
1 u = 56 ÷ 2 = 28
Number of girls = 28
Answer(s): (a) 139 cm; (b) 28