Class W, X and Y were given some sweets to sell for their donation drive. The average number of sweets the 3 classes had at first was 236. After Class X sold thrice as many sweets as Class W and Class Y sold ⁶₇ as many sweets as Class X, the average number of sweets the 3 classes had left was 52. How many sweets did Class W and Class Y sell altogether?

Class W	Class X	Class Y
1x7	3x7
	7x3	6x3
7 u	21 u	18 u

Class W : Class X : Class Y
7 : 21 : 18

Total number of sweets that the 3 classes had at first
= 3 x 236
= 708

Number of sweets that the 3 classes left
= 3 x 52 
= 156

Number of sweets that were sold by 3 classes
= 708 - 156
= 552

7 u + 21 u + 18 u = 552
46 u = 552

1 u = 552 ÷ 46 = 12

Total number of sweets sold by Class W and Class Y
= 7 u + 18 u
= 25 u
= 25 x 12
= 300

Answer(s): 300