5 min read
2026-02-27
Proportions are one of the most versatile tools in math. These tips help you solve problems quickly and accurately.
Ask: if one quantity increases, does the other increase or decrease? Direct — both increase together; inverse — one goes up as the other goes down.
All values in the proportion must use the same units. Convert km to m or hours to minutes before you set up the proportion.
In a/b = c/d, an unknown x can be found with cross products. Memorize this as multiplying “on the diagonal.”
If a recipe needs 200 g of flour for 4 servings, you need more for 8, not less. Always check that the direction of change matches the story.
“Find 35% of 800” is a proportion: 35/100 = x/800, so x = 280.
For linked quantities, build a chain — for example speed → time → distance — and solve step by step.
In practice you often round. Round up for material margins and down when there are hard limits.
See also: Fraction Calculator, Equation Solver, GCD and LCM