Class Q, R and S were given some mini cupcakes to sell for their charity drive. The average number of mini cupcakes the 3 classes had at first was 247. After Class R sold four times as many mini cupcakes as Class Q and Class S sold ⁴₅ as many mini cupcakes as Class R, the average number of mini cupcakes the 3 classes had left was 42. How many mini cupcakes did Class Q and Class S sell altogether?

Class Q	Class R	Class S
1x5	4x5
	5x4	4x4
5 u	20 u	16 u

Class Q : Class R : Class S
5 : 20 : 16

Total number of mini cupcakes that the 3 classes had at first
= 3 x 247
= 741

Number of mini cupcakes that the 3 classes left
= 3 x 42 
= 126

Number of mini cupcakes that were sold by 3 classes
= 741 - 126
= 615

5 u + 20 u + 16 u = 615
41 u = 615

1 u = 615 ÷ 41 = 15

Total number of mini cupcakes sold by Class Q and Class S
= 5 u + 16 u
= 21 u
= 21 x 15
= 315

Answer(s): 315