30 students in a class sold an average of 15 stamps for charity. There were 6 more girls than boys in the class. The average number of stamps sold by the girls was 13. Find the average number of stamps sold by the boys.
| |
Boys |
Girls |
Total |
| Number |
1 u |
1 u + 6 |
30 |
| Value |
? |
13 |
15 |
| Total value |
216 |
234 |
450 |
Total number of stamps sold
= 30 x 15
= 450
Number of boys = 1 u
Number of girls = 1 u + 6
1 u + 1 u + 6 = 30
2 u + 6 = 30
2 u = 30 - 6
2 u = 24
1 u = 24 ÷ 2 = 12
Number of girls in class
= 1 u + 6
= 12 + 6
= 18
Number of stamps sold by girls
= 18 x 13
= 234
Number of stamps sold by boys
= 450 - 234
= 216
Average number of stamps sold by boys
= 216 ÷ 12
= 18
Answer(s): 18
