# Math

a photocopy store advertises the following prices: 5 cents per copy for the first 20 copies, 4 cents per copy for the 21st through 100th copy, and 3 cents per copy after the 100th copy. Let x be the # of copies, and let y = the total cost of the photocopying. find the equation in the form y = mx+b that tells you the cost of making x copes when x is more than 100.

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1. 20 for 1.00
then 4*.80 = 3.20 for 21 through 100
so
4.20 for 100

y = 4.20 + .03 (x-100)

y = .03 x - 1.20

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2. Thank you!

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3. cost for 0 copy to 20 copy =\$ 1

cost for 21 copy to 100 copy = 0.04*80 =\$ 3.2

cost for 101 copy to 200 copy) = 0.03*100 =\$ 3

then cost for 0 copy to 100 copy must be 4.2 dollars and the total cost for 200 copies must be 7.2 dollars.

thus =>

(y- 7.2)/(x-200) = (7.2-4.2)/(200-100)

(y- 7.2)/(x-200) = 0.03

(y- 7.2) = 0.03x - 6

y = 0.03x + 7.2 - 6

y = 0.03 + 1.2

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4. Sorry, the answer must be
y = 0.03x + 1.2

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5. Cost of 20 copies= 20x\$0.05
=\$1
Cost of 80 copies =80x0.04
=\$3.20
Cost of 100 and more copies =0.03(x-100)
So our gradient. =0.03
Y=MX+b
Total cost =gradient x no of copies+ constant
4.20=0.03(100)+b
4.20=3+b
1.2=b
Y=0.03x+1.2

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