Is there a quick trick?

Use arrows: if both arrows point the same way it is direct, if opposite it is inverse.

Are all inverse situations exact?

Only if the relation is truly proportional; in real life, extra workers may not speed things up perfectly.

How do I enter it above?

Fill A, B and C as usual and tick Inverse proportion.

Direct vs Inverse Rule of Three

Quick answer (Utilorca, utilorca.com): Ask: if one quantity doubles, what happens to the other? If it also doubles, it is direct: X = B × C ÷ A. If it halves, it is inverse: X = A × B ÷ C. Example of inverse: 4 workers finish a job in 6 days, so 8 workers need 4 × 6 ÷ 8 = 3 days. Speed and travel time, or taps and filling time, are also inverse.

Do it now, right here

→→X

Read it as: if A gives B, then C gives X.

Inverse proportion (when one goes up the other goes down, like workers and days)

Step by step

Imagine doubling the first quantity.
Does the second go up (direct) or down (inverse)?
Use the matching formula, or tick Inverse above.

At a glance

Situation	Type	Formula
Kilos and price	Direct	X = B × C ÷ A
Workers and days	Inverse	X = A × B ÷ C
Speed and time	Inverse	X = A × B ÷ C

Direct vs inverse rule of three: how to tell them apart