Ratio, proportion and rates of changeKS3 / GCSE

Using a direct proportion equation

Substitute or rearrange a direct proportion equation.

  • In direct proportion, is constant.
  • Use , where is a constant.
  • Use the given equation to find either variable.

Example 1

The quantities satisfy . Find when .

Simplify the numerical terms and collect like terms.

Example 2

The quantities satisfy . Find the positive value of when .

Apply this to both sides; then write the subject on the left.Simplify the numerical terms and collect like terms.

Your turn

Question 1

The quantities satisfy . Find when .

Check answer
Simplify the numerical terms and collect like terms.
Question 2

The quantities satisfy . Find the positive value of when .

Check answer
Apply this to both sides; then write the subject on the left.Simplify the numerical terms and collect like terms.
Question 3

The quantities satisfy . Find when .

Check answer
Simplify the numerical terms and collect like terms.
Question 4

The quantities satisfy . Find the positive value of when .

Check answer
Apply this to both sides; then write the subject on the left.Simplify the numerical terms and collect like terms.
Question 5

The quantities satisfy . Find when .

Check answer
Simplify the numerical terms and collect like terms.
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