PSLE
Tina bought some jelly beans and gave half of it to Luis. Luis bought some chocolate bars and gave half of it to Tina. Tina ate 7 chocolate bars and Luis ate 9 jelly beans. The ratio of Tina's chocolate bars to jelly beans became 1 : 6 and the ratio of Luis's chocolate bars to jelly beans became 1 : 3. How many jelly beans did Tina buy?

	Tina		Luis
	Chocolate bars	Jelly beans	Chocolate bars	Jelly beans
Before	1 u + 7	6 u	1 p	3 p + 9
Change	- 7			- 9
After	1 u	6 u	1 p	3 p

After Tina gave half of the jelly beans to Luis and Luis gave half of his chocolate bars to Tina, Luis and Tina had same number of chocolate bars and jelly beans before each ate some.

6 u = 3 p + 9 
6 u - 9 = 3 p --- (1)

1 u + 7 = 1 p --- (2)

Make p the same.

(2)_x3
3 u + 21 = 3 p --- (3)

(1) = (3)
6 u - 9 = 3 u + 21 
6 u - 3 u = 21 + 9
3 u = 30

1 u = 30 ÷ 3 = 10

Number of jelly beans that Tina bought
= 2 x 6 u
= 12 u
= 12 x 10
= 120

Answer(s): 120