Need Help On Math Question

Question

Serge is choosing a cell phone plan and wants the lowest cost. Cell-a-Bration charges $12 per month plus $0.05 per minute for cell phone service. E-Phone charges $28 per month for unlimited minutes.

Determine under which conditions Serge should choose Cell-a-Bration and under which conditions Serge should choose E-Phone.

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I don't understand and I have to plot this on a graph as "Monthly cost vs. Number of Minutes" as the title, "Number of minutes" on the x axis and "Monthly cost ($)" on the y axis.

Answer 1

12 +.05M = 28

.05M = 16

M=16/.05 = 320 minutes per month makes both plans cost the same

If you use more than 320 minutes, use E-phone

if you use less than 320 minutes per month, use Cele-Bration

plot the first cost as C=12+.05M with M on the x axis and C on the y axis

It's a straight line with a y intercept of 12 and almost flat line with slope 1/20

the second E-phone cost is a flat horizontal line C=28, slope =0 and y intercept of 28. they intersect at (M,C) the point (320,28)