SOLUTION: The monthly cost (in dollars) of water use (in dollars) is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 17 HCF of water is $34

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Question 697428: The monthly cost (in dollars) of water use (in dollars) is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 17 HCF of water is $34.47 , and the cost for using 45 HCF is $80.67 . What is the cost for using 25 HCF of water?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Basically, they are giving you 2 points on a graph, and
they want you to find a 3rd point.
Plot hundreds of ft3 ( HFC ) on the horizontal axis
and Monthly cost on the vertical axis.
---------------
Given:
( 17, 34.47 ) and
( 45, 80.67 )
------------
Let +c+ = Monthly cost of water use
Let +h+ = HFC's of water
------------
Use the general point-slope formula
+%28+c+-+34.47+%29+%2F+%28+h+-+17+%29+=+%28+80.67+-+34.47+%29+%2F+%28+45+-+17+%29+
+%28+c+-+34.47+%29+%2F+%28+h+-+17+%29+=+46.2+%2F+28+
+28%2A%28+c+-+34.47+%29+=+46.2%2A%28+h+-+17+%29+
+28c+-+965.16+=+46.2h+-+785.4+
+28c+=+46.2h+%2B+179.76+
+c+=+1.65h+%2B+6.42+ answer
-------------------
check answer:
Does the line include ( 45, 80.67 )
+c+=+1.65h+%2B+6.42+
+80.67+=+1.65%2A45+%2B+6.42+
+80.67+=+74.25+%2B+6.42+
+80.67+=+80.67+
OK- you can check ( 17, 34.47 )
----------------------------
What is the cost for using 25 HCF of water?
+c+=+1.65%2A25+%2B+6.42+
+c+=+41.25+%2B+6.42+
+c+=+47.67+
The cost is $47.67