Is it proportional?
Type numbers into the table. Each row is one point on the graph. The blue line goes through zero and the point from row 1. If every other point sits on that line, the table is proportional. The last column shows y ÷ x for each row, so you can see why.
| x | y | y ÷ x |
|---|
Use numbers that are 0 or more. Decimals such as 2.5 are fine.
What's going on
Two amounts are proportional when doubling one doubles the other, tripling one triples the other, and so on. That happens exactly when y ÷ x gives the same number in every row. That one number ties the whole table together: y is always that number times x.
On a graph, a proportional table makes a straight line that passes through zero. Both parts matter. Press "Example: no" to see points in a perfectly straight line that still fail the test, because the line misses zero. Zero of one thing must mean zero of the other.
Try it: make a table for "3 pens cost 4 dollars". Then change one y by a tiny amount and watch that point step off the line.
Sheet: Is it proportional?