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Ratio Simplifier

Same-direction change

Direct Proportion Calculator

Use one known pair of values to calculate the matching value when two quantities are directly proportional.

Calculate the corresponding value

If x and y are directly proportional, y/x stays constant.

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Formula: y₂ = y₁ × (x₂ ÷ x₁). Equivalently, y = kx where k is constant.

Example

If 3 units correspond to 12 units, then 5 units correspond to 12 × 5 ÷ 3 = 20.

When to use direct proportion

Use direct proportion when increasing one quantity by a factor increases the other by the same factor—for example quantity and cost at a fixed unit price.

How direct proportion works

Start with a known pair. x₁ and y₁ give the constant relationship.
Find the scale factor. Divide x₂ by x₁.
Apply the same factor to y. y₂ = y₁ × x₂/x₁.
General proportionSolve any missing value in a/b = c/d.Inverse proportionOne value rises while the other falls.Equivalent ratiosGenerate and check equal ratios.

Direct proportion FAQs

What is direct proportion?

Two quantities are directly proportional when multiplying one by a factor multiplies the other by the same factor.

What is the direct proportion formula?

Use y = kx. With a known pair, k = y₁/x₁ and the new value is y₂ = y₁ × x₂/x₁.

Can I use fractions or decimals?

Yes. Whole numbers, decimals and fractions such as 3/4 are accepted.