Basic Math & Pre-Algebra Workbook For Dummies with Online Practice
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Cross-multiplication is a handy tool for finding the common denominator for two fractions, which is important for many operations involving fractions. In the following practice questions, you are asked to cross-multiply to compare fractions to find out which is greater or less.

Practice questions

1. Find the lesser fraction:


2. Among these three fractions, which is greatest:


Answers and explanations

1. Of the two fractions,


Cross-multiply to compare the two fractions:


Because 35 is less than 36,


2. Of the three fractions,


Use cross-multiplication to compare the first two fractions.


Because 21 is greater than 20, this means that 1/10 is greater than 2/21, so you can rule out 2/21. Next, compare 1/10 and 3/29 by cross-multiplying.


Because 30 is greater than 29, 3/29 is greater than 1/10. Therefore, 3/29 is the greatest of the three fractions.

About This Article

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About the book author:

Mark Zegarelli is a math and test prep teacher who has written a wide variety of basic math and pre-algebra books in the For Dummies series.

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