Question

Shelby, Allen, and Denise printed their digital photos. Each requested the same size prints. Shelby paid $2.70 for 5 prints. Allen paid $3.24 for 11 prints. Denise paid $4.05 for 20 prints.

Describe how you would write the equation for the relationship between the number of photos ordered and the amount paid.

Answer 1

Let n = number of photos and C = total cost (dollars). Assume a fixed fee a plus b dollars per print: C = a + b n.

Use two data points to find a and b. From Shelby: a + 5b = 2.70. From Allen: a + 11b = 3.24.
Subtract: 6b = 0.54 so b = 0.09. Then a = 2.70 − 5(0.09) = 2.25.

So the equation is C = 2.25 + 0.09n (i.e., $2.25 service fee plus $0.09 per print).