# maths

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The Number Two Plumbing Co. charges \$45 per hour plus a fixed service call charge of \$65. Write an equation that will allow you to compute the total bill for any number of hours, x, that it takes to complete a job.
A. C = 45x + 65
B. C = 65x + 45
C. 65x + 45C = 0
D. 45x + 65C = 0

A business purchases a copier for \$5,500 and anticipates it will be worth \$2,500 after 10 years. Use straight-line depreciation to find a linear model for the depreciated value V of the copy machine after t years of use.
A. V = -5,500 + 300t
B. V = 300 - 5500t
C. V = -300 + 5500t
D. V = 5,500 - 300t

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#1. Since there is a fixed charge of \$65, you know that there will be a "...+65" in the solution. That leaves only (A)

#2 Since the value starts at \$5500, you know the solution will have "5500-..." in it. That leaves only (D)

See whether you can justify the rest of the solution.

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A for the 1st one, 45 dollars per hour, x, is 45x. The fixed-service is a one-time thing so it's c = 45x + 65.The 2nd one is D. The original cost of the copier is 5,500. 5500-2500 = 3000. This is the cost reduction over the ten years. 3000/10 is 300: The amount it gets reduced by every year. For D, when you plug in 10, you get 2,500.

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thanks much Steve and Kelsi