Inverse Rule of Three Calculator
Runs 100% in your browser — your files never leave your device.
Some quantities move in opposite directions: more workers, fewer days; faster speed, less travel time. The inverse rule of three finds the missing fourth value when the product stays constant. Type the three values you know and the answer appears instantly.
How it works
- 1
Enter the known pair
Amount A and amount B — for example, 3 workers and 4 days.
- 2
Enter the new amount
The changed quantity — for example, 6 workers.
- 3
Read the result
The counterpart appears live — 6 workers take 2 days.
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