Olivia buys a dress, a jumpsuit, a skirt and a jacket. The average cost of these items is $21. The total cost of the skirt and the jacket is ³₄ of the total cost of the dress and the jumpsuit. If the dress costs $11.80 and the jacket costs $13.20, find the difference in cost between the jumpsuit and the skirt.
Total cost of the 4 items
= 4 x 21
= $84

Total cost of the skirt and the jacket = 3 u
Total cost of the dress and the jumpsuit = 4 u

Total cost of the 4 items
= 3 u + 4 u
= 7 u

7 u = 84

1 u = 84 ÷ 7 = 12

Total cost of the skirt and the jacket
= 3 u
= 3 x 12
= $36

Cost of the skirt
= 36 - 13.20
= $22.80

Total cost of the dress and the jumpsuit
= 4 u
= 4 x 12
= $48

Cost of the jumpsuit
= 48 - 11.80
= $36.20

Difference in cost between the jumpsuit and the skirt
= 36.20 - 22.80
= $13.40

Answer(s): $13.40