LEI - Creating Linear Equations to Solve Problems (Lesson)

Creating Linear Equations to Solve Problems

Let's go back to our introduction question: You pay $40 a month to get 5GB of data to use for your phone. Last month, you went over by 35 MB and you are charged $0.50 per MB. How much do you owe?

So we know that we owe $40 plus an additional $0.50 x 35 = $17.50 so a total of $57.50.

Could you write an equation for any amount of data used?

Let x = MB of data used over 5GB. So then you know you would owe $40 plus an additional $.50 times x. So our linear equation is C = $0.5x + 40.

Notice a few things about this equation:

It is linear because the degree of x is 1. We introduced a new variable, C, which represents the total cost of the bill. Now you can plug in any value for x to figure out your cost.

Use the equation above to determine the following: If your bill was $60 last month, how many extra MB did you use?

Let C = 60 since we know that was the total cost. The unknown, or question is how many MB did we use, which is what we defined x to be:

60 = 0.5x + 40

-40            -40

20 = 0.5x

20/0.5 = 0.5x/0.5

x = 40

So we know that you used 40 extra MB during that month.
Watch this video to try a few different examples:

Write and Solve Linear Equations Practice

IMAGES CREATED BY GAVS