PSLE
The pupils at a camp are divided in Group A and Group B. The ratio of the number of girls to boys in Group A is 7 : 3. The ratio of the number of girls to boys in Group B is 5 : 1. There are 3 times as many pupils in Group B as in Group A. There are 270 less girls in Group A than Group B. What is the total number of pupils in Group A?

Group A		Group B
10 u		6x5 = 30 u
Girls	Boys	Girls	Boys
7 u	3 u	5x5 = 25 u	1x5 = 5 u

Total number of pupils in Group A
= 7 u + 3 u
= 10 u

Total number of pupils in Group B
= 3 x 10 u
= 30 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 30 and 6 is 30.

Number of less girls in Group A than Group B
= 25 u - 7 u
= 18 u

18 u = 270

1 u = 270 ÷ 18 = 15

Total number of pupils in Group A
= 7 u + 3 u
= 10 u
= 10 x 15
= 150

Answer(s): 150