Proportion Calculator
Enter three known values below to instantly solve the proportion for x.
Solve a/b = c/x for x
/=/ x
x
12
Solving a Proportion
For a/b = c/x, cross-multiply: x = (b × c) ÷ a.
Worked example
Solve 3/4 = 9/x.
x = (4 × 9) ÷ 3 = 36 ÷ 3
x = 12
Frequently Asked Questions
How do you solve a proportion?
Cross-multiply: for a/b = c/x, that gives a × x = b × c, so x = (b × c) ÷ a.
What is a proportion in math?
A proportion is a statement that two ratios are equal, written as a/b = c/d. Solving one means finding a missing value that keeps both ratios equivalent.
What's a real-world example of a proportion?
Scaling a recipe (if 2 cups of flour makes 12 cookies, how much flour makes 30 cookies?) or converting a scale drawing to real-world size are both proportion problems.
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