PSLE
Mary bought some lollipops and gave half of it to Dylan. Dylan bought some jelly beans and gave half of it to Mary. Mary ate 10 jelly beans and Dylan ate 20 lollipops. The ratio of Mary's jelly beans to lollipops became 1 : 6 and the ratio of Dylan's jelly beans to lollipops became 1 : 2. How many lollipops did Mary buy?

	Mary		Dylan
	Jelly beans	Lollipops	Jelly beans	Lollipops
Before	1 u + 10	6 u	1 p	2 p + 20
Change	- 10			- 20
After	1 u	6 u	1 p	2 p

After Mary gave half of the lollipops to Dylan and Dylan gave half of his jelly beans to Mary, Dylan and Mary had same number of jelly beans and lollipops before each ate some.

6 u = 2 p + 20 
6 u - 20 = 2 p --- (1)

1 u + 10 = 1 p --- (2)

Make p the same.

(2)_x2
2 u + 20 = 2 p --- (3)

(1) = (3)
6 u - 20 = 2 u + 20 
6 u - 2 u = 20 + 20
4 u = 40

1 u = 40 ÷ 4 = 10

Number of lollipops that Mary bought
= 2 x 6 u
= 12 u
= 12 x 10
= 120

Answer(s): 120