Solve proportions with the rule of three: enter A, B and C to find X, with a switch for inverse proportion problems like workers versus hours.
The rule of three finds a missing value when three values of a proportion are known. Enter value A, the value B it corresponds to, and a new value C, and the tool shows the unknown X. In the default direct mode, X equals B times C divided by A, which suits recipes, unit prices or map scales.
Tick Inverse Proportion Mode when one quantity goes down as the other goes up, such as more workers needing fewer hours. In that mode X equals A times B divided by C. Results are rounded to two decimal places and update as you type.
Use it when increasing one quantity decreases the other, for example speed and travel time, or number of workers and hours to finish a job.
X = (B × C) ÷ A. For example, if 5 items cost 100, then 12 items cost 240.