The average height of a group of girls was 154 cm. After 9 boys with a total of 1521 cm joined the group, the average height of all the pupils increased to 159 cm.
- What was the average height of the boys?
- How many girls were there in the group?
|
Girls |
Boys |
Pupils |
Number |
1 u |
9 |
1 u + 9 |
Value |
154 |
? |
159 |
Total value |
154 u |
1521 |
159 u + 1431 |
(a)
Average height of boys
= 1521 ÷ 9
= 169 cm
(b)
Total height of pupils
= 159(1 u + 9)
= 159 u + 1431
Total height of girls and boys = 154 u + 1521
159 u + 1431 = 154 u + 1521
159 u - 154 u = 1521 - 1431
5 u = 90
1 u = 90 ÷ 5 = 18
Number of girls = 18
Answer(s): (a) 169 cm; (b) 18