Compare two fractions with different numerators and different denominators, e.g., by creating common denominators or numerators, or by comparing to a benchmark fraction such as 1/2. Recognize that comparisons are valid only when the two fractions refer to the same whole. Record the results of comparisons with symbols >, =, or <, and justify the conclusions, e.g., by using a visual fraction model.
When given any two fractions and asked to compare, it is sometimes difficult to determine which fraction is greater than another fraction. This is especially the case when the two fractions don't share a common denominator. For the purposes of this post, I am going to assume the students that I am working with are familiar with the concept of a common denominator and how to find one.
However, given two fractions without common denominators, how can we compare the two?
Visual Model Method
One way to compare two fractions would be to draw a picture and then make a comparison based upon your drawing. This method is not always the best route to take when working with paper and pencil. However, a computer program that gives you exact measurements can show this method with great ease. To work with this method, follow this link to an activity and work the problems listed in the google document.
Common Denominator Method
The second way to compare two fractions is to find a common denominator and then compare the numerators. A common denominator can alway be found by multiplying the denominators of both fractions. For example, to compare 1/2 and 3/8, we can give the two fractions the common denominator 2 x 8 = 24 in order to compare them. In order to represent 1/2 in units of twenty-fourths, you must multiply the numerator and denominator by 12. Thus, showing that 1/2 is equivalent to 12/24. Then, you must represent 3/8 in units of twenty-fourths. To do so, you must multiply the numerator and denominator by 3. Thus, showing that 3/8 is equivalent to 9/24. Since 9 units of 1/24 is smaller than 12 units of 1/24, then one can assume that 12/24 is greater than 9/24 (12/24 > 9/24). Follow this link to an activity containing a further explanation and problems to solve using this method.
Benchmark Method
The final way to compare fractions is to compare each fraction to a particular "benchmark" fraction. Some examples of good benchmark fractions are 1/4, 1/3, 1/2, and 1. In order to use this method, it is perhaps best to use the given fractions as units of length so that you can say that the fraction that is the closest distance to the benchmark (without surpassing the benchmark) is the greater of the two. Follow this link to view a video and work with this method.
So there you have it...three different ways to compare fractions. If you're a student who'd like more practice or an instructor who's looking for more supplemental activities for your kids, the following games should suit your needs: