The average height of a group of boys was 164 cm. After 7 girls with a total of 1176 cm joined the group, the average height of all the pupils increased to 165 cm.
- What was the average height of the girls?
- How many boys were there in the group?
|
Boys |
Girls |
Pupils |
Number |
1 u |
7 |
1 u + 7 |
Value |
164 |
? |
165 |
Total value |
164 u |
1176 |
165 u + 1155 |
(a)
Average height of girls
= 1176 ÷ 7
= 168 cm
(b)
Total height of pupils
= 165(1 u + 7)
= 165 u + 1155
Total height of boys and girls = 164 u + 1176
165 u + 1155 = 164 u + 1176
165 u - 164 u = 1176 - 1155
1 u = 21
1 u = 21 ÷ 1 = 21
Number of boys = 21
Answer(s): (a) 168 cm; (b) 21