John bought 5 times as many dark chocolate bars as white chocolate bars. The total mass of dark chocolate bars and white chocolate bars was 2130 g. The mass of white chocolate bars was 810 g less than that of the dark chocolate bars. The mass of 1 white chocolate bar was 61 g heavier than 1 dark chocolate bar.

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

	Dark Chocolate Bars	White Chocolate Bars	Total
Number of sets	5 sets	1 set
Compare each	1 u	1 u + 61
Total value	1470 g	660 g	2130 g

(a)
Mass of white chocolate bars = 1 set
Mass of dark chocolate bars = 5 sets

Mass of white chocolate bars = (2130 - 810) ÷ 2 = 660 g
Mass of dark chocolate bars = 660 + 810 = 1470 g

Mass of 1 set of white chocolate bars = 660 g
Mass of 1 set of dark chocolate bars = 1470 ÷ 5 = 294 g

Difference in the mass between 1 set of white chocolate bars and 1 set of dark chocolate bars
= 660 - 294
= 366 g

Number of items in each set
= 366 ÷ 61
= 6

Number of dark chocolate bars
= 5 x 6
= 30

(b)
Mass of 1 white chocolate bar
= 660 ÷ 6
= 110 g

Answer(s): (a) 30; (b) 110 g