Class B, C and D were given some mochi balls to sell for their charity drive. The average number of mochi balls the 3 classes had at first was 214. After Class C sold four times as many mochi balls as Class B and Class D sold ⁴₅ as many mochi balls as Class C, the average number of mochi balls the 3 classes had left was 50. How many mochi balls did Class B and Class D sell altogether?

Class B	Class C	Class D
1x5	4x5
	5x4	4x4
5 u	20 u	16 u

Class B : Class C : Class D
5 : 20 : 16

Total number of mochi balls that the 3 classes had at first
= 3 x 214
= 642

Number of mochi balls that the 3 classes left
= 3 x 50 
= 150

Number of mochi balls that were sold by 3 classes
= 642 - 150
= 492

5 u + 20 u + 16 u = 492
41 u = 492

1 u = 492 ÷ 41 = 12

Total number of mochi balls sold by Class B and Class D
= 5 u + 16 u
= 21 u
= 21 x 12
= 252

Answer(s): 252