Rule of Three
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Tap a term to see what it means, or .
Calculate
Example: 3 kg of cheese cost 45. How much do 5 kg cost? Switch to inverse proportion and read it as: 3 builders take 45 days; how many days would 5 take? Change the values to work out your own case.
Step by step
What each term means
- Value Sought (y₂)
- The value of y that matches the new x₂.
- Known Value (y₁)
- The y of the known case.
- New x (x₂)
- The new quantity. In a direct proportion, y grows by the same ratio as x: x₂/x₁.
- Known x (x₁)
- The x of the known case. In an inverse proportion, the fraction flips, y₂ = y₁ · x₁/x₂, because the product x · y stays constant.