Using equations to represent linear relationships
About this video
A cell phone plan costs a flat $25 per month plus $7 for each gigabyte of data. The video writes the total monthly cost as y = 25 + 7x, where x is the number of gigabytes used.
You'll be able to
- write a linear equation from a situation with a flat fee and a cost per unit.
- explain what each number in y = 25 + 7x means.
Key words
- flat fee
- A fixed amount you pay no matter how much you use.
- variable
- A letter, like x or y, that stands for a quantity that can change.
Transcript
- [Instructor] A cell phone plan charges a flat fee of $25 per month plus $7 for each gigabyte of data used. Let x be the number of gigabytes used in a month, and let y be the total monthly cost in dollars. Write an equation that represents the total monthly cost, y, when x gigabytes are used.
So pause the video, have a go at that. All right. So we want to write an equation for y; that's our total monthly cost. Well, we know that we pay $25 a month no matter what, no matter how many gigabytes we use, so it's going to be 25, and then it's going to be plus however many gigabytes we use times seven.
So x is the gigabytes used times seven, so that's going to be plus 7x, and we're done.
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