21 children in a class sold an average of 20 cards for charity. There were 7 more boys than girls in the class. The average number of cards sold by the boys was 18. Find the average number of cards sold by the girls.
|
Girls |
Boys |
Total |
Number |
1 u |
1 u + 7 |
21 |
Value |
? |
18 |
20 |
Total value |
168 |
252 |
420 |
Total number of cards sold
= 21 x 20
= 420
Number of girls = 1 u
Number of boys = 1 u + 7
1 u + 1 u + 7 = 21
2 u + 7 = 21
2 u = 21 - 7
2 u = 14
1 u = 14 ÷ 2 = 7
Number of boys in class
= 1 u + 7
= 7 + 7
= 14
Number of cards sold by boys
= 14 x 18
= 252
Number of cards sold by girls
= 420 - 252
= 168
Average number of cards sold by girls
= 168 ÷ 7
= 24
Answer(s): 24