Question

How do I write an equation for #17?

Answer 1

16.95x + .05y = 22.95x + .02y

Answer 2

let's say we have two phone companies, A and B, A charges $16.95 monthly and $0.05 a minute, B $22.95 monthly and $0.2 a minute.

company A

1 minute...................... $16.95 + 0.05(1)

2 minutes.................... $16.95 + 0.05(2)

3 minutes.................... $16.95 + 0.05(3)

x minutes.................... $16.95 + 0.05(x)

company B

1 minute...................... $22.95 + 0.02(1)

2 minutes.................... $22.95 + 0.02(2)

3 minutes.................... $22.95 + 0.02(3)

x minutes.................... $22.95 + 0.02(x)

when will the cost of each plan be the same?  well, that happens when 16.95 +0.05x = 22.95 + 0.02x.

$\bf \stackrel{A}{16.95+0.05x}=\stackrel{B}{22.95+0.02x}\implies 0.05x-0.02x=22.95-16.95 \\\\\\ 0.03x=6\implies x=\cfrac{6}{0.03}\implies x=200$