Suppose that a household's monthly water bill (in dollars) is a linear function of the amount of water the household uses (in hundreds of cubic feet, HCF). When graphed, the function gives a line with a slope of 1.45.
If the monthly cost for 20 HCF is 24.38 , what is the monthly cost for 25 HCF?

Question

Suppose that a household's monthly water bill (in dollars) is a linear function of the amount of water the household uses (in hundreds of cubic feet, HCF). When graphed, the function gives a line with a slope of  1.45. 
If the monthly cost for  20 HCF is 24.38  , what is the monthly cost for 25 HCF?

anonymous · Answer

ok they give you the slope so now you need the y intercept. do you know how you could find it?

anonymous · Answer

not a clue =/

anonymous · Answer

ok no problem lets make a function C(x) = 1.45x + ??

anonymous · Answer

you know C(20) = 24.38

anonymous · Answer

Can you find the y intercept now. Remeber that linear functions look like f(x) = mx + b where m is the slope and b is the y intercept. 

They are asking you to find how much the water company charges even if you use no water

anonymous · Answer

the y intercept would be the answer then?

anonymous · Answer

Well you have to find what the function is. Then you can plug the number 25 into your function and see how much it costs to use 25 units of water

anonymous · Answer

look at it this way. 1.45 is the slope meaning it costs 1.45 dollars per unit of water.

1.45 * 20 = 29 but your question says it only costs 24.38

why is this?