Question

A cellular phone company offers a contract for which the cost C, in dollars, of t minutes of telephoning is given by C=0.25(t-500)+ 56.95, where it is assumed that t is greater than or equal to 500 minutes. What times will keep cost between $92.20 and $129.95?

Answer 1

C = .25(t - 500) + 56.95
C = .25t - 125 + 56.95
C = .25t - 68.05
C + 68.05 = .25t
(C + 68.05) / .25 = t

(92.2 + 68.05) / .25 = t
641 = t

(129.95 + 68.05) / .25 = t
792 = t
Is this right?

Answer 2

Solve 92.20 = 0.25(t-500)+56.95 t≥500
0.25(t-500)=92.2-56.95
t-500=(92.2-56.95)/0.25
t=500+(92.20-56.95)/0.25=641

Similarly, solve for t in
129.95=0.25(t-500)+56.95
to get t=792.

The posted answers are right, well done!

Answer 3

Thank you

Answer 4

You're welcome!