Class S, T and U were given some mochi balls to sell for their fund-raising project. The average number of mochi balls the 3 classes had at first was 220. After Class T sold twice as many mochi balls as Class S and Class U sold ³₄ as many mochi balls as Class T, the average number of mochi balls the 3 classes had left was 49. How many mochi balls did Class S and Class U sell altogether?

Class S	Class T	Class U
1x2	2x2
	4x1	3x1
2 u	4 u	3 u

Class S : Class T : Class U
2 : 4 : 3

Total number of mochi balls that the 3 classes had at first
= 3 x 220
= 660

Number of mochi balls that the 3 classes left
= 3 x 49 
= 147

Number of mochi balls that were sold by 3 classes
= 660 - 147
= 513

2 u + 4 u + 3 u = 513
9 u = 513

1 u = 513 ÷ 9 = 57

Total number of mochi balls sold by Class S and Class U
= 2 u + 3 u
= 5 u
= 5 x 57
= 285

Answer(s): 285