Jane buys a sweater, a jumpsuit, a dress and a shirt. The average cost of these items is $30. The total cost of the dress and the shirt is ³₅ of the total cost of the sweater and the jumpsuit. If the sweater costs $15.80 and the shirt costs $7.10, find the difference in cost between the jumpsuit and the dress.
Total cost of the 4 items
= 4 x 30
= $120

Total cost of the dress and the shirt = 3 u
Total cost of the sweater and the jumpsuit = 5 u

Total cost of the 4 items
= 3 u + 5 u
= 8 u

8 u = 120

1 u = 120 ÷ 8 = 15

Total cost of the dress and the shirt
= 3 u
= 3 x 15
= $45

Cost of the dress
= 45 - 7.10
= $37.90

Total cost of the sweater and the jumpsuit
= 5 u
= 5 x 15
= $75

Cost of the jumpsuit
= 75 - 15.80
= $59.20

Difference in cost between the jumpsuit and the dress
= 59.20 - 37.90
= $21.30

Answer(s): $21.30