Match the Quantities
Make sure each numerator and denominator compares quantities in the same order.
Free Interactive Math Tool
Solving Proportions Practice
Find missing values in equivalent ratios using scale factors or cross multiplication, then apply proportions to real-world situations.
Learn How Equivalent Ratios and Cross Products Work
Learn how to keep corresponding quantities in the same order, choose a solving method, isolate the unknown, and verify your answer.
Read the Solving Proportions GuideHow It Works
Solve for the Missing Value
A proportion states that two ratios are equal. Your job is to find the value that keeps them equivalent.
Choose a Method
Use a scale factor when it is easy to see, or use cross multiplication for any proportion.
Solve for the Unknown
Complete the equivalent ratio or divide the cross product to isolate the missing value.
Check the Proportion
Substitute your answer and confirm that the ratios simplify to the same value.
Interactive Practice
Solve the Proportion
Correct
0
Problems
0
Streak
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Cross Multiplication
MediumSolve for x.
3
4
x
20
Your Response
Find the missing value.
Enter the value of x. Use a decimal when the answer is not a whole number.
Correct!
You found the value that makes the ratios equivalent.
Proportion
3/4 = x/20
Answer
x = 15
Cross multiply: 4x = 3 × 20. Divide both sides by 4 to get x = 15.
Helpful Strategies
Keep Both Ratios Equivalent
Whether you use a scale factor or cross multiplication, the goal is to preserve the relationship between the corresponding quantities.
Use the Same Order
If the first ratio is miles per hour, the second ratio must also place miles above hours.
Look for a Scale Factor
Multiply or divide both parts of one ratio by the same number to produce an equivalent ratio.
Cross Multiply
Multiply diagonally to form an equation, then use division to isolate the unknown value.
Substitute and Check
Replace x with your answer and verify that both ratios have the same decimal or simplified form.
Real-World Applications
Where Proportions Appear
Recipes and Serving Sizes
Scale ingredient amounts while keeping every ratio in a recipe the same.
Maps and Scale Drawings
Convert a measurement on a map, model, or drawing into the corresponding actual distance or size.
Prices and Unit Rates
Find an unknown cost or quantity when the price per item remains constant.
Similar Figures
Use corresponding side lengths to find missing measurements in similar shapes.
Practice Another Proportion
Generate another problem to practice recognizing corresponding quantities, selecting a method, and checking that the two ratios are equivalent.