A gym costs $25 plus $12.50 per visit. Write the equation.

Step by step

The question

Question: A gym costs $25 plus $12.50 per visit.

Write the equation.

1 Which depends on which

The cost depends on the number of visits.

So x is the visits: the input.

y is the cost: the output.

2 Rate of change

Rate of change means: how much y changes when x goes up by 1.

Each visit, it goes up by 12.5.

So m is 12.5.

3 Start value

The start value is y when x is 0.

At the start, with 0 visits, it is 25.

Careful!

The 12.5 is per visit: it goes with x.

The 25 is only once.

4 Write the equation

A line is y = m x plus b: m is the rate of change, b is the start value.

So the equation is y = 12.5x + 25.

5 Check

Let's check with 4 visits: the equation gives 75.

In the story: 25, plus 12.5, plus 12.5, plus 12.5, plus 12.5: 75.

So the answer is right!

Let's look back.

First: which depends on which.

Then: rate of change.

Then: start value.

Then: write the equation.

Last: check.