Question

The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 15 HCF of water is 32.84, and the cost for using 43 HCF is 79.04. What is the cost for using 36 HCF of water?

Answer 1

67.49

Explanation:

Let the number of HCF be x.

Let the cost be y.

You are given 2 points of a line: (15, 32.84) and (43, 79.04).

Now we find the equation of the line that passes through those points.

y - y1 = m(x - x1)

y - 32.84 = [(79.04 - 32.84)/(43 - 15)](x - 15)

y - 32.84 = (46.2/28)(x - 15)

y - 32.84 = 1.65(x - 15)

y = 1.65x - 24.75 + 32.84

y = 1.65x + 8.09

Now we let x = 36 and solve for y.

y = 1.65(36) + 8.09

y = 67.49