Cross Multiply in Ratios  Learn  Contents and Search  Practice  Next Lesson  Play  Previous Lesson  Explore   Feedback Practice Your Spelling List States of the United States Nations of the World   Cross multiplication to solve proportions A proportion is an equation which states that two ratios are equal. When the terms of a proportion are cross multiplied, the cross products are equal. Cross multiplication is the multiplication of the numerator of the first ratio by the denominator of the second ratio and the multiplication of the denominator of the first ratio by the numerator of the second ratio. 21 3 -- = -- 70 10 21 * 10 = 70 * 3 210 = 210 If one term of a proportion is not known, cross multiplication can be used to find the value of that term. x 3 -- = -- 70 10 x * 10 = 70 * 3 10x = 210 10x 210 --- = --- 10 10 x = 21 Return to Top Share Practice Unit Rates Determine the value of x by cross multiplying.  If    =         Then x   =   You have correct and   incorrect.  This is percent correct. Return to Top Tell Others About This Site AAASpell.com Practice Your Spelling List Practice Our Spelling Lists Vocabulary Practice Alphabet Practice Play Game What is it? Best Score How many correct answers can you get in 60 seconds? Extra time is awarded for each correct answer. Play longer by getting more correct. How fast can you get 20 more correct answers than wrong answers? Sudoku Timez Attack Multiplication Video Game Return to Top Explore Math Lessons by Grade Kindergarten  First Second Third Fourth Fifth Sixth Seventh Eighth Math Topics Addition Algebra Comparing Counting Decimals Division Equations Estimation Exponents Fractions Geometry Graphs Measurement Mental Math Money Multiplication Naming Numbers Patterns Percent Place Value Practical Math Properties Ratios Statistics Subtraction Math Resources Schools Teachers Parents Home Schooling Web Resources Spelling Lessons by Grade First Second Third Fourth Fifth Sixth Seventh Eighth or - Practice Your Word List Vocabulary Lessons by Grade First Second Third Fourth Fifth Sixth Seventh Eighth Geography States of the United States Nations of the World Geographical Photos WorldPlenty.com What will the future be like? Other Interests Music DVD Computer and Video Games Books Sports Toys and Games Return to Top About This Site Frequently Asked Questions Send Us Feedback About this Site Privacy Policy Purchase The Math Class CD Share| Return to Top