PSLE The pupils at a school choir are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 7 : 1. The ratio of the number of boys to girls in Group B is 5 : 7. There are 3 times as many pupils in Group B as in Group A. There are 39 more boys in Group B than Group A. What is the total number of girls?
Group A |
Group B |
8 u |
12x2 = 24 u |
Boys |
Girls |
Boys |
Girls |
7 u |
1 u |
5x2 = 10 u |
7x2 = 14 u
|
Total number of pupils in Group A
= 7 u + 1 u
= 8 u
Total number of pupils in Group B
= 3 x 8 u
= 24 u
The total number of pupils in Group B is repeated.
Use LCM to make the total number of pupils in Group B the same.
LCM of 24 and 12 is 24.
Number of more boys in Group B than Group A
= 10 u - 7 u
= 3 u
3 u = 39
1 u = 39 ÷ 3 = 13
Total number of girls
= 1 u + 14 u
= 15 u
= 15 x 13
= 195
Answer(s): 195