Class D, E and F were given some sweets to sell for their fund-raising project. The average number of sweets the 3 classes had at first was 240. After Class E sold four times as many sweets as Class D and Class F sold ⁷₈ as many sweets as Class E, the average number of sweets the 3 classes had left was 53. How many sweets did Class D and Class F sell altogether?

Class D	Class E	Class F
1x2	4x2
	8x1	7x1
2 u	8 u	7 u

Class D : Class E : Class F
2 : 8 : 7

Total number of sweets that the 3 classes had at first
= 3 x 240
= 720

Number of sweets that the 3 classes left
= 3 x 53 
= 159

Number of sweets that were sold by 3 classes
= 720 - 159
= 561

2 u + 8 u + 7 u = 561
17 u = 561

1 u = 561 ÷ 17 = 33

Total number of sweets sold by Class D and Class F
= 2 u + 7 u
= 9 u
= 9 x 33
= 297

Answer(s): 297