# 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.

asked by P
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

posted by Damon
2. Thank you!

posted by P

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

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

posted by Uthpala

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