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Rule of three calculator step by step

Calculate a simple, direct or inverse rule of three instantly. If A is equivalent to B, what is C equivalent to? We solve it step by step.

A \u2192 B  ;  C \u2192 x

Practice exercises on regla de tres

How how the rule of three works

In a direct rule of three (more is more: more kilos, higher price), the unknown value is x = (B · C) / A. In an inverse one (more is less: more workers, fewer days), it is x = (A · B) / C.

Setup: "A is equivalent to B; C is equivalent to x".

ExampleIf 3 kg cost €6, how much do 5 kg cost? (direct)

Step-by-step solution

  1. Direct: x = (B · C) / A = (6 · 5) / 3.
  2. We calculate: 30 / 3 = 10.
Result: 5 kg cost €10.

Don't just focus on the result: learn how to do it

With Refuerzo.ai you practice the rule of three with hundreds of exercises and instant feedback that explains why. Try for free, no card required.

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Frequently asked questions

How do I know if the rule of three is direct or inverse?

It is direct if increasing one quantity increases the other (kilos and price). It is inverse if increasing one decreases the other (workers and days, speed and time).

Can it be used to calculate percentages?

Yes, a percentage is a direct rule of three over 100. For example, 20% of 150 is x = (20 · 150) / 100 = 30.

Is the calculator free?

Yes, the the rule of three calculator is free. And if you want to practice with hundreds of instantly corrected exercises, you have a 5-day trial with no card required on Refuerzo.ai.