PSLE
The students at a sports meet are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 7 : 5. The ratio of the number of boys to girls in Group B is 7 : 1. There are 2 times as many students in Group B as in Group A. There are 112 more boys in Group B than Group A. What is the total number of girls?

Group A		Group B
12 u		8x3 = 24 u
Boys	Girls	Boys	Girls
7 u	5 u	7x3 = 21 u	1x3 = 3 u

Total number of students in Group A
= 7 u + 5 u
= 12 u

Total number of students in Group B
= 2 x 12 u
= 24 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 24 and 8 is 24.

Number of more boys in Group B than Group A
= 21 u - 7 u
= 14 u

14 u = 112

1 u = 112 ÷ 14 = 8

Total number of girls
= 5 u + 3 u
= 8 u
= 8 x 8
= 64

Answer(s): 64