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 13 HCF of water is $36.18, and the cost for using 39 HCF is $76.48. What is the cost for using 36 HCF of water? Monthly cost (in dollars) ? Water usage (in HCF)

Answer 1

As 13 hcf cost $36.18 and 39 hcf cost $76.48 and this form a linear equation thus coordinates are (13,36.18) and (39,76.48)

Slope of line =(76.48-36.18)/(39-13)

= 40.3/26

= 1.55

The line is form of

y=1.55x+c

Here (13,36.18) are point on this thus plug in this

36.18= 1.55*13+c

Gives, c= 36.18-20.15 = 16.03

The overall equation becames

y= 1.55x+16.03

For x= 36

y = 1.55*36+16.03

y= 71.83

Thus it cost $71.83 for 36 hcf of water