Question

Your phone plan charges you an initial fee, and then a certain amount depending on the amount of data you use. They send you periodic updates of your usage and your current bill cost. After using 3 GB of data, you owe $30. After 5 GB of data, you owe $40. What is the cost per GB of data?

Answer 1

$5

Explanation:

Let

x = initial fee

y = fees depending on the amount of data he use

After using 3 GB of data , he owes $30.

After using 5 GB of data , he owes $40.

The equations are

x + 3y = 30 (1)

x + 5y = 40 (2)

Subtract (1) from (2) to eliminate x

5y - 3y = 40 - 30

2y = 10

Divide both sides by 2

y = 10/2

y = $5

Substitute y = 5 into (1)

x + 3y = 30

x + 3(5) = 30

x + 15 = 30

x = 30 - 15

x = $15

Cost per GB of data = $5