Problema Solution
A basic cell phone plan costs $25 per months for 60 calling minutes. Additional time costs $.90 per minute. Formula C=25+0.90(x-60) gives the monthly cost for this plan, C, for x calling minutes, where x>60. How many calling minutes are possible for a monthly cost of at least $79 and at most $160?
Answer provided by our tutors
First we calculate the number of minutes for a monthly cost of $79:
C = 79
That is we need to solve the equation:
25+0.90(x-60) = 79
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click here to see the equation solved for x
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x = 120 min
The number of minutes for a monthly cost of $160 is calculated by solving the equation:
25+0.90(x-60) = 160
........
click here to see the equation solved for x
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x = 210 min
The number of possible minutes is in a closed interval from 120 minutes to 210 minutes.