PSLE
The students at a sports meet 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 4 : 1. There are 2 times as many students in Group B as in Group A. There are 63 more girls in Group B than Group A. What is the total number of boys?

Group A		Group B
10 u		5x4 = 20 u
Girls	Boys	Girls	Boys
7 u	3 u	4x4 = 16 u	1x4 = 4 u

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

Total number of students in Group B
= 2 x 10 u
= 20 u

The total number of students in Group B is repeated.
Use LCM to make the total number of students in Group B the same.
LCM of 20 and 5 is 20.

Number of more girls in Group B than Group A
= 16 u - 7 u
= 9 u

9 u = 63

1 u = 63 ÷ 9 = 7

Total number of boys
= 3 u + 4 u
= 7 u
= 7 x 7
= 49

Answer(s): 49