PSLE
The number of girls and boys in a tuck shop were in the ratio 2 : 5. After 6.5 girls entered the tuck shop and half the number of boys left the tuck shop, the ratio of the number of girls to boys became 1 : 1. How many children were there in the tuck shop at first?

	girls	boys	Total
Before	2 u	5 u	7 u
Change	+ 6.5	- 2.5 u
After	2 u + 6.5	2.5 u

Number of boys who left the tuck shop
= 5 u ÷ 2
= 2.5 u

Number of girls in the end = 2 u + 6.5
Number of boys in the end = 2.5 u

Since the ratio of the number of girls to boys in the end is 1 : 1, the number of girls and boys in the end is equal.

2.5 u = 2 u + 6.5
2.5 u - 2 u = 6.5
0.5 u = 6.5

1 u = 6.5 ÷ 0.5 = 13

Total number of children in the tuck shop at first
= 2 u + 5 u
= 7 u
= 7 x 13
= 91

Answer(s): 91