Class R, S and T 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 238. After Class S sold thrice as many mochi balls as Class R and Class T sold ⁶₇ as many mochi balls as Class S, the average number of mochi balls the 3 classes had left was 54. How many mochi balls did Class R and Class T sell altogether?

Class R	Class S	Class T
1x7	3x7
	7x3	6x3
7 u	21 u	18 u

Class R : Class S : Class T
7 : 21 : 18

Total number of mochi balls that the 3 classes had at first
= 3 x 238
= 714

Number of mochi balls that the 3 classes left
= 3 x 54 
= 162

Number of mochi balls that were sold by 3 classes
= 714 - 162
= 552

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

1 u = 552 ÷ 46 = 12

Total number of mochi balls sold by Class R and Class T
= 7 u + 18 u
= 25 u
= 25 x 12
= 300

Answer(s): 300