PSLE
On Wednesday, the number of adults to girls to boys visiting a zoo was 7 : 12 : 4. On Thursday, the number of adults visiting the zoo remained the same. However, the number of girls decreased by 25% and the number of boys increased by 25%.

1. What was the ratio of the number of children to adults visiting the zoo on Thursday?
2. On Wednesday, 400 girls and boys visited the zoo. What was the total number of child visitors at the zoo on Thursday?

	Adults	Girls	Boys
Before	7 u	12 u	4 u
Change		- 3 u	+ 1 u
After	7 u	9 u	5 u

(a)
Increase in the number of girls
= 25% x 12 u
= ²⁵₁₀₀ x 12 u
= 3 u

Decrease in the number of boys
= 25% x 4 u
= ²⁵₁₀₀ x 4 u
= 1 u

Number of girls on Thursday
= 12 u - 3 u
= 9 u

Number of boys on Thursday
= 4 u + 1 u
= 5 u

Number of children on Thursday
= 9 u + 5 u
= 14 u

On Thursday
Children : Adults
14 : 7

(b)
Number of girls and boys on Wednesday
= 12 u + 4 u
= 16 u

16 u = 400

1 u = 400 ÷ 16 = 25

Total number of child visitors on Thursday
= 14 u
= 14 x 25
= 350

Answer(s): (a) 14 : 7; (b) 350