PSLE
Ivory bought some chocolate bars and gave half of it to Bobby. Bobby bought some sweets and gave half of it to Ivory. Ivory ate 3 sweets and Bobby ate 8 chocolate bars. The ratio of Ivory's sweets to chocolate bars became 1 : 6 and the ratio of Bobby's sweets to chocolate bars became 1 : 4. How many sweets did Bobby buy?

	Ivory		Bobby
	Sweets	Chocolate bars	Sweets	Chocolate bars
Before	1 u + 3	6 u	1 p	4 p + 8
Change	- 3			- 8
After	1 u	6 u	1 p	4 p

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

6 u = 4 p + 8 
6 u - 8 = 4 p --- (1)

1 u + 3 = 1 p --- (2)

Make p the same.

(2)_x4
4 u + 12 = 4 p --- (3)

(1) = (3)
6 u - 8 = 4 u + 12 
6 u - 4 u = 12 + 8
2 u = 20

1 u = 20 ÷ 2 = 10

1 p
= 1 u + 3
= 10 + 3
= 13

Number of sweets that Bobby bought
= 2 p
= 2 x 13
= 26

Answer(s): 26