PSLE
Kathy bought some lollipops and gave half of it to Andy. Andy bought some chocolate bars and gave half of it to Kathy. Kathy ate 2 chocolate bars and Andy ate 5 lollipops. The ratio of Kathy's chocolate bars to lollipops became 1 : 5 and the ratio of Andy's chocolate bars to lollipops became 1 : 2. How many chocolate bars did Andy buy?

	Kathy		Andy
	Chocolate bars	Lollipops	Chocolate bars	Lollipops
Before	1 u + 2	5 u	1 p	2 p + 5
Change	- 2			- 5
After	1 u	5 u	1 p	2 p

After Kathy gave half of the lollipops to Andy and Andy gave half of his chocolate bars to Kathy, Andy and Kathy had same number of chocolate bars and lollipops before each ate some.

5 u = 2 p + 5 
5 u - 5 = 2 p --- (1)

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

Make p the same.

(2)_x2
2 u + 4 = 2 p --- (3)

(1) = (3)
5 u - 5 = 2 u + 4 
5 u - 2 u = 4 + 5
3 u = 9

1 u = 9 ÷ 3 = 3

1 p
= 1 u + 2
= 3 + 2
= 5

Number of chocolate bars that Andy bought
= 2 p
= 2 x 5
= 10

Answer(s): 10