# Directly Proportional

## Contents

## Key Stage 4

### Meaning

When two variables are **directly proportional** when one variable is multiplied by a factor, the other variable is multiplied by the same factor.

### About Direct Proportionality

- A scatter graph showing a
**directly proportional**relationship has line with a linear gradient that passes through zero (it has a y-intercept of zero). - On a proportional scatter graph when one variable doubles, the other doubles or when one triples the other triples.
- When two variables are
**directly proportional**when any value for y is divided by its corresponding value for x it will always give a constant value. - Two variables are said to be
**directly proportional**when they always vary by the same ratio.

### Exam Marks

- Straight line [1 mark]
- Passing through zero / passing through the origin [1 mark]

### Examples

This scatter graph shows a linear relationship that is directly proportional where x doubles, y doubles.
\(y = mx\) Where m, the gradient, is positive. |

### References

#### AQA

*Directly proportional, pages 158-159, 282, GCSE Physics; Third Edition, Oxford University Press, AQA*