The average number of boys in 5A, 5B and 5C is 15. This is 4 more than the average number of girls in the 3 rooms.
211 of the total number of girls are in 5C.
52 of the number of girls in 5B is the same as
511 of the total number of girls in the 3 rooms. What fraction of the total number of boys in the 3 rooms is in 5A if there are 36 pupils in 5A?
| Girls in 5A |
Girls in 5B |
Girls in 5C |
Total girls |
| 9 |
2 |
11 |
| |
2 |
|
11 |
| 7 u |
2 u |
2 u |
11 u |
52 of girls in 5B =
511 of all girls
Girls in 5B : All girls = 2 : 11
Average number of girls
= 15 - 4
= 11
Total number of girls
= 3 x 11
= 33
11 u = 33
1 u = 33 ÷ 11 = 3
Number of girls in Room 5A
= 7 u
= 7 x 3
= 21
Number of boys in Room 5A
= 36 - 21
= 15
Total number of boys
= 3 x 15
= 45
Boys in 5ATotal boys =
1545 =
13 Answer(s):
13 
