PSLE
Anna bought some sweets and gave half of it to Tommy. Tommy bought some chocolate bars and gave half of it to Anna. Anna ate 6 chocolate bars and Tommy ate 21 sweets. The ratio of Anna's chocolate bars to sweets became 1 : 5 and the ratio of Tommy's chocolate bars to sweets became 1 : 2. How many sweets did Anna buy?

	Anna		Tommy
	Chocolate bars	Sweets	Chocolate bars	Sweets
Before	1 u + 6	5 u	1 p	2 p + 21
Change	- 6			- 21
After	1 u	5 u	1 p	2 p

After Anna gave half of the sweets to Tommy and Tommy gave half of his chocolate bars to Anna, Tommy and Anna had same number of chocolate bars and sweets before each ate some.

5 u = 2 p + 21 
5 u - 21 = 2 p --- (1)

1 u + 6 = 1 p --- (2)

Make p the same.

(2)_x2
2 u + 12 = 2 p --- (3)

(1) = (3)
5 u - 21 = 2 u + 12 
5 u - 2 u = 12 + 21
3 u = 33

1 u = 33 ÷ 3 = 11

Number of sweets that Anna bought
= 2 x 5 u
= 10 u
= 10 x 11
= 110

Answer(s): 110