Question

Two cell phone companies have different rate plans. Runfast has monthly charges $25 plus $10 per gig of data. B A &D’s monthly charge is $18 plus 15 per gig of data. Your task is to determine under what circumstances each company has the better pricing.

Okay I am trying to do the substitution method for this problem. I found their monthly prices and put them in an equation like it asked.

25+10x-RunFast

18+15x-BA&D

I need help with solving these equations using the substitution method. I got 132-150x for 25+10x, but I am pretty sure that is over the top incorrect. I have no idea how to do this, and help would be really appreciated.

Answer 1

let the number of gigs used be g

Runfast:
cost = 25 + 10g

BA&D:
cost = 18+15g

let's see for how many g's the plans are the same
cost of one = cost of the other
18+15g = 25+10g
5g = 7
g = 7/5 = 1.4 gigs

so for 0 gigs over, BA&D would cost $18 vs $25 for Runfast, so

BA&D is the better plan if you stay below 1.4 gigs
and Runfast is better if your use more than 1.4 gigs

Answer 2

thanks:) I totally needed the help!