Class B, C and D were given some mochi balls to sell for their donation drive. The average number of mochi balls the 3 classes had at first was 216. After Class C sold thrice as many mochi balls as Class B and Class D sold ³₄ as many mochi balls as Class C, the average number of mochi balls the 3 classes had left was 41. How many mochi balls did Class B and Class D sell altogether?

Class B	Class C	Class D
1x4	3x4
	4x3	3x3
4 u	12 u	9 u

Class B : Class C : Class D
4 : 12 : 9

Total number of mochi balls that the 3 classes had at first
= 3 x 216
= 648

Number of mochi balls that the 3 classes left
= 3 x 41 
= 123

Number of mochi balls that were sold by 3 classes
= 648 - 123
= 525

4 u + 12 u + 9 u = 525
25 u = 525

1 u = 525 ÷ 25 = 21

Total number of mochi balls sold by Class B and Class D
= 4 u + 9 u
= 13 u
= 13 x 21
= 273

Answer(s): 273