Is it proportional: x 10, 20, 30, 40; y 15, 30, 45, 60

Step by step

The question

Question: is this table proportional: x is 10, 20, 30, 40, and y is 15, 30, 45, 60?

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

We call that number k.

Then y = k times x.

We write it as a table.

1 Divide y by x

For each pair we work out y divided by x.

15/10 is 1.5.

30/20 is 1.5.

45/30 is 1.5.

60/40 is 1.5.

2 Compare the answers

The same number every time.

So it is proportional, and k = 1.5.

3 Write the equation

y = k x, with k = 1.5.

So the equation is y = 1.5x.

4 Check

Let's check: k times x should give each y.

1.5 times 10 is 15.

1.5 times 20 is 30.

1.5 times 30 is 45.

1.5 times 40 is 60.

So the answer is right!

Let's look back.

First: divide y by x.

Then: compare the answers.

Then: write the equation.

Last: check.