Class M, N and P were given some sweets to sell for their fund-raising project. The average number of sweets the 3 classes had at first was 231. After Class N sold twice as many sweets as Class M and Class P sold ⁷₈ as many sweets as Class N, the average number of sweets the 3 classes had left was 41. How many sweets did Class M and Class P sell altogether?

Class M	Class N	Class P
1x4	2x4
	8x1	7x1
4 u	8 u	7 u

Class M : Class N : Class P
4 : 8 : 7

Total number of sweets that the 3 classes had at first
= 3 x 231
= 693

Number of sweets that the 3 classes left
= 3 x 41 
= 123

Number of sweets that were sold by 3 classes
= 693 - 123
= 570

4 u + 8 u + 7 u = 570
19 u = 570

1 u = 570 ÷ 19 = 30

Total number of sweets sold by Class M and Class P
= 4 u + 7 u
= 11 u
= 11 x 30
= 330

Answer(s): 330