Question

Denise's cell phone plan is $29.95 per month plus $.10 per minute for each minute over 300 minutes of call time. Denise's cell phone bill is $99.95. For how many minutes was she billed? Answer is 700 but what is the algebraic equation?

Answer 1

cost = .10(m-300) + 29.95 , where m is the number of minutes

so ....
.10(m-300) + 29.95 = 99.95
.1m - 30 = 70
.1m = 100
m = 100/.1 = 1000

She used 1000 minutes, but is only billed for any time over 300 minutes , look at (m-300) in the equation.
She was billed for 700 minutes

btw, the equation is only valid for m>300
if m<300
it would simply be
cost = 29.95