Oliver bought 4 times as many white chocolate bars as dark chocolate bars. The total mass of white chocolate bars and dark chocolate bars was 2844 g. The mass of dark chocolate bars was 684 g less than that of the white chocolate bars. The mass of 1 dark chocolate bar was 71 g heavier than 1 white chocolate bar.

1. Find the number of dark chocolate bars that Oliver bought.
2. Find the mass of 1 white chocolate bar.

	White Chocolate Bars	Dark Chocolate Bars	Total
Number of sets	4 sets	1 set
Compare each	1 u	1 u + 71
Total value	1764 g	1080 g	2844 g

(a)
Mass of dark chocolate bars = 1 set
Mass of white chocolate bars = 4 sets

Mass of dark chocolate bars = (2844 - 684) ÷ 2 = 1080 g
Mass of white chocolate bars = 1080 + 684 = 1764 g

Mass of 1 set of dark chocolate bars = 1080 g
Mass of 1 set of white chocolate bars = 1764 ÷ 4 = 441 g

Difference in the mass between 1 set of dark chocolate bars and 1 set of white chocolate bars
= 1080 - 441
= 639 g

Number of items in each set
= 639 ÷ 71
= 9

Number of dark chocolate bars
= 1 x 9
= 9

(b)
Mass of 1 dark chocolate bar
= 1080 ÷ 9
= 120 g

Mass of 1 white chocolate bar
= 120 - 71
= 49 g

Answer(s): (a) 9; (b) 49 g