Marion buys a vest, a coat, a skirt and a sweater. The average cost of these items is $27. The total cost of the skirt and the sweater is ⁴₅ of the total cost of the vest and the coat. If the vest costs $12.80 and the sweater costs $18.40, find the difference in cost between the coat and the skirt.
Total cost of the 4 items
= 4 x 27
= $108

Total cost of the skirt and the sweater = 4 u
Total cost of the vest and the coat = 5 u

Total cost of the 4 items
= 4 u + 5 u
= 9 u

9 u = 108

1 u = 108 ÷ 9 = 12

Total cost of the skirt and the sweater
= 4 u
= 4 x 12
= $48

Cost of the skirt
= 48 - 18.40
= $29.60

Total cost of the vest and the coat
= 5 u
= 5 x 12
= $60

Cost of the coat
= 60 - 12.80
= $47.20

Difference in cost between the coat and the skirt
= 47.20 - 29.60
= $17.60

Answer(s): $17.60