math
posted by melissa on .
MaineCellular offers a phone plan that costs $12 per month plus 10 cents per minute. Portland Wireless offers a plan that costs $20 per month plus 5 cents per minute. How many minutes could you use in a month so that it would cost less to use the MaineCellular plan? Be specific in your answer  give the full range of minutes that answers the question.

X = the cost of MaineCellular's plan
P = the cost of Portland Wireless' plan
T = time in minutes.
X = $12 + $0.10 T
P = $20 + $0.05 T
P = X at the number of minutes that the two costs cross. So, set X = P
$12 + $0.10 T = $20 + $0.05 T
Solve for T.
Once you have T, anything less than T minutes will give one of the plans an edge. Which one?
Anything greater than T minutes will give the other plan the edge.