There is a brick grill in the backyard, Bob and Carol are going to make a concrete patio in the shape of a trapezoid next to the grill. The concrete slab needs to be at least 2 inches thick. They will use 40 pound bags of premixed concrete. Each 40-pound bag makes 0.30 cubic feet of concrete and costs $6.50. How much will the materials cost, including the 7.5% tax?

  $48.91

Step-by-step explanation:

The area of the patio is given by the area formula for a trapezoid:

  A = (1/2)(b1 +b2)(h)

  A = (1/2)(2 +6)(3) = 12 . . . . square feet.

If the slab is 2 inches thick, the volume is ...

  V = Bh = (12 ft²)(2 in/(12 in/ft)) = 2 ft³

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The number of bags required will be ...

  (2 ft³)/(0.3 ft³/bag) = 6 2/3 bags

We assume that only whole bags can be purchased, so the project will require (at least) 7 bags of premixed concrete.

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The cost for 7 bags is ...

  (7 bags)($6.50/bag)(1 +7.5%) = $45.50×1.075 ≈ $48.91

The material cost for the concrete mix will be $48.91.