PSLE
At first, the ratio of the number of boys to the number of girls in a kindergarten was 7 : 4. After 35 boys and 35 girls joined the kindergarten, the ratio became 4 : 3.

1. Did the percentage of students who were girls increase (1), decrease (2) or remain the same (3)? Give your answer in number. (Eg Increase = 1)
2. In the end, how many boys were there in the kindergarten?

	Boys	Girls	Difference	Total
Before	7x1  = 7 u	4x1 = 4 u	3x1 = 3 u	7 u + 4 u = 11 u
Change	+ 35	+ 35
After	4x3 = 12 u	3x3 = 9 u	1x3 = 3 u	12 u + 9 u = 21 u

(a)
35 boys and 35 girls joined the kindergarten. There was equal number of boys and girls who joined the kindergarten.

Since the increase in number of students in both groups is the same, the difference between the number of boys and girls remains unchanged.

We make the difference between the number of boys and girls at first and in the end the same.
LCM of 3 and 1 = 3 u

Percent of students who were girls at first
= ⁴₁₁ x 100%
≈ 36% (Round off to whole number.)

Percent of students who are girls in the end
= ⁹₂₁ x 100%
≈ 43% (Round off to whole number.)

Percent of students who were girls increased from 36% to 43%. (1)

(b)
Increase in the number of boys
= 12 u - 7 u
= 5 u

5 u = 35

1 u = 35 ÷ 5 = 7

Number of boys in the end
= 12 u
= 12 x 7
= 84

Answer(s): (a) 1; (b) 84