Basic Math and Pre-Algebra For Dummies (39 page)

You can use cross-multiplication to compare fractions and find out which is greater. When you do so, make sure that you start with the numerator of the first fraction.

 To find out which of two fractions is larger, cross-multiply and place the two numbers you get, in order, under the two fractions. The larger number is always under the larger fraction. In this case, 14 goes under
and 12 goes under
. The number 14 is greater than 12, so
is greater than
.

For example, suppose you want to find out which of the following three fractions is the greatest:

Cross-multiplication works only with two fractions at a time, so pick the first two —
and
— and then cross-multiply:

Because 27 is greater than 25, you know now that
is greater than
. So you can throw out
.

Now do the same thing for
and
: