Kevin plans to put concrete on a rectangular portion of his driveway. the portion is 10 feet long and three inches high. the price of concrete is $98 per cubic yard. the total cost of the concrete kevin needs is $72.59. which of the following is closest to the width of the portion of the driveway on which kevin plans to put concrete?
[1 foot = 12 inches; 1 yard = 3 feet]
3 feet
6 feet
8 feet
10 feet

The correct answer is 8 ft.

Explanation:
We start out by finding out the number of cubic feet of concrete used.
The cost of the concrete he used is $72.59. Since concrete is $98 per cubic yard, this means he uses less than 1 cubic yard. We divide 72.95/98 to find out what portion of a cubic yard he uses: 72.95/98 = 0.74 cu. yd.

Since the measurements of the driveway are given in feet and inches, we will change 0.74 cu. yd. to cubic feet. 1 cubic yard is a cube with length, width and height all 1 yd. 1 yd = 3ft, so the measurements of the cube are 3ft by 3ft by 3ft; this makes a volume of 27 cu. ft. We need 0.74 cu. yd. of concrete; 0.74*27 = 19.98 cu. ft.

We know that the volume of a rectangular prism is V=lwh. We have V=19.98, l=10, and h=3/12=0.25 (3 inches out of 12 inches it takes to make a foot). This leaves our width, w, unknown, and gives us the equation
19.98=10w(0.25).

Simplifying the right hand side gives us
19.98=2.5w.

Divide both sides by 2.5:
19.98/2.5 = 2.5w/2.5
7.992=w.

This rounds to 8 feet.

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