Lucy buys a skirt, a blouse, a sweater and a shirt. The average cost of these items is $34. The total cost of the sweater and the shirt is ³₅ of the total cost of the skirt and the blouse. If the skirt costs $19.90 and the shirt costs $15.80, find the difference in cost between the blouse and the sweater.
Total cost of the 4 items
= 4 x 34
= $136

Total cost of the sweater and the shirt = 3 u
Total cost of the skirt and the blouse = 5 u

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

8 u = 136

1 u = 136 ÷ 8 = 17

Total cost of the sweater and the shirt
= 3 u
= 3 x 17
= $51

Cost of the sweater
= 51 - 15.80
= $35.20

Total cost of the skirt and the blouse
= 5 u
= 5 x 17
= $85

Cost of the blouse
= 85 - 19.90
= $65.10

Difference in cost between the blouse and the sweater
= 65.10 - 35.20
= $29.90

Answer(s): $29.90