Question

The graph below represents c, the amount a phone company charges, based on m, the number of minutes the customer uses each month. If there are a maximum of 44,640 minutes in a month, which equation best represents the phone company’s monthly charges?

A graph entitled Phone Company Charges has number of minutes on the x-axis and cost in dollars on the y-axis. The line has a positive slope and goes through (0, 15) and (40, 25).

c = StartFraction 15 Over m EndFraction, 0 less-than m less-than-or-equal-to 44,640
c = one-fourth m + 15, 0 less-than-or-equal-to m less-than-or-equal-to 44,640
c = 15 + StartFraction 4 Over m EndFraction, 0 less-than m less-than-or-equal-to 44,640
c = 15 m + one-fourth, 0 less-than-or-equal-to m less-than-or-equal-to 44,640

Answer 1

Find the slope: (25 − 15)/(40 − 0) = 10/40 = 1/4, and the y‑intercept is 15. So the equation is c = (1/4)m + 15 with 0 ≤ m ≤ 44,640.