One cell phone plan costs $39.95 per month. The first 500 minutes of usage are free. Each minute thereafter costs $.35. Write a rule that describes the total monthly cost as a function of the number of minutes of usage (over 500 minutes). Then find the number of minutes of usage over 500 minutes for a bill of $69.70?

Question

anonymous · Answer

Let c=cost
and m=minutes of usage(over 500 minutes)

c=.35m+39.95

anonymous · Answer

So to find the number of minutes over 500 for a bill of $69.70, substitute 69.70 into the equation for c and solve for m

anonymous · Answer

c = $39.95 + $0.35 e

Now to find the number of minutes over 500 in a bill of $69.7

$69.7 = $39.95 + $0.35 e
$29.75 = $0.35e
$29.75 / $0.35 = e
85 min = e

The person talked an extra 85 min over 500 min, or a total of 585 minutes used.

anonymous · Answer

Yep