Class K, L and M were given some chocolate bars to sell for their fund-raising project. The average number of chocolate bars the 3 classes had at first was 218. After Class L sold thrice as many chocolate bars as Class K and Class M sold ⁷₈ as many chocolate bars as Class L, the average number of chocolate bars the 3 classes had left was 59. How many chocolate bars did Class K and Class M sell altogether?

Class K	Class L	Class M
1x8	3x8
	8x3	7x3
8 u	24 u	21 u

Class K : Class L : Class M
8 : 24 : 21

Total number of chocolate bars that the 3 classes had at first
= 3 x 218
= 654

Number of chocolate bars that the 3 classes left
= 3 x 59 
= 177

Number of chocolate bars that were sold by 3 classes
= 654 - 177
= 477

8 u + 24 u + 21 u = 477
53 u = 477

1 u = 477 ÷ 53 = 9

Total number of chocolate bars sold by Class K and Class M
= 8 u + 21 u
= 29 u
= 29 x 9
= 261

Answer(s): 261