Direct proportion means both quantities move in the same direction: when one increases, the other increases in the same ratio.
Use this calculator when your relationship is “more → more” (or “less → less”), like price vs quantity or distance vs time at constant speed.
Direct Rule of Three Calculator
As one quantity increases, the other increases proportionally.
Formula: x = (b × c) ÷ a
corresponds to
then
corresponds to
Quick Example
If 2 apples cost $6, how much do 5 apples cost?
Set \(a = 2\), \(b = 6\), \(c = 5\). Then \(x = (b \times c) \div a = (6 \times 5) \div 2 = 15\).
Not sure if it’s direct or inverse?
If your problem is “more workers → less time”, that’s inverse. Use the inverse proportion calculator.