# Constructing a linear function.

• Jul 7th 2011, 08:45 PM
sardorbek
Constructing a linear function.
A photocopy store advertises the following prices: 5/c per copy for the first 20 copies, 4/c per
copy for the 21st through 100th copy, and 3/c per copy after the 100th copy. Let
x be the
number of copies, and let
y be the total cost of photocopying. (a) Graph the cost as x goes
from 0 to 200 copies. (b) Find the equation in the form
y = mx + b that tells you the cost
of making
x copies when x is more than 100

• Jul 7th 2011, 10:50 PM
CaptainBlack
Re: I cant solve this simple problem
Quote:

Originally Posted by sardorbek
A photocopy store advertises the following prices: 5/c per copy for the first 20 copies, 4/c per
copy for the 21st through 100th copy, and 3/c per copy after the 100th copy. Let
x be the
number of copies, and let y be the total cost of photocopying. (a) Graph the cost as x goes
from 0 to 200 copies. (b) Find the equation in the form y = mx + b that tells you the cost
of making x copies when x is more than 100

The graph consists of three line segments the first for 0 to 20 copies of slope 5c per copy. The second from 20 to 100 copies with slope 4c per copy starting from where the first segment ended. The third segment runs from 100 to 200 copies with a slope of 3c per copy starting from where the second segment ended.

CB
• Jul 8th 2011, 02:42 AM
sardorbek
Re: I cant solve this simple problem
Thank you for explanation,
I tried to solve it but my answer was wrong. Answer should be according to the book y=0.03x+1.2.
Does this function intersect at 1.2??
• Jul 8th 2011, 07:09 AM
HallsofIvy
Re: I cant solve this simple problem
It's impossible to tell what you did wrong if you don't show what you did or even what result you got!

How much will it cost to make 100 copies? that is 20 at 5 c each, 80 at 4 c each.

How many will it cost to make 200 copies? Again, that is 20 at 5c each and 80 at 4 c each, plus 100 at 3 c each. Once you know the cost for 100 and 200,
put those as "y" values in y1= m(100)+ b and y2= m(200)+ b and solve for m and b.

(Yes, the y-intercept of this function is \$1.20.)
• Jul 8th 2011, 07:53 AM
CaptainBlack
Re: I cant solve this simple problem
Quote:

Originally Posted by sardorbek
Thank you for explanation,
I tried to solve it but my answer was wrong. Answer should be according to the book y=0.03x+1.2.
Does this function intersect at 1.2??

Did you do the first part and plot the graph?

..and as Halls asked what was your answer and argument to support it?

By the way the book answer is wrong unless there is more in the question than you posted. The question is formulated in cents but the book answer given in dollars, now if it says it wants the answer in dollars that is different.

CB
• Jul 10th 2011, 09:11 PM
sardorbek
Re: Constructing a linear function.
Thank you HallsofIvy.
I am agree with Captain Black. The question is not asked either in dollar or cent.
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