5 rides cost $12 and 10 rides cost $20. Is the cost proportional to…

Step by step

The question

Question: 5 rides cost $12, and 10 cost $20: is the cost proportional to the number of rides?

Let x be the number of rides.

Let y be the cost.

Proportional means: y divided by x is always the same number.

We call that number k.

Then y = k times x.

1 Divide y by x

For each pair we work out y divided by x.

12/5 is 2.4.

20/10 is 2.

2 Compare the answers

The answers are not the same.

So it is not proportional.

Careful!

y goes up by the same amount each time.

But that is not enough.

y divided by x must stay the same.

3 Check

Let's check: the first two pairs already give different answers.

So the answer is right!

Let's look back.

First: divide y by x.

Then: compare the answers.

Last: check.