Basic Math and Pre-Algebra For Dummies (41 page)

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Authors: Mark Zegarelli

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You can make this problem easier by canceling out the number 13, as follows:

You can make it even easier by noticing that 20 and 5 are both divisible by 5, so you can also factor out the number 5 before multiplying:

One is the easiest number

With fractions, the relationship between the numbers, not the actual numbers themselves, is most important. Understanding how to multiply and divide fractions can give you a deeper understanding of why you can increase or decrease the numbers within a fraction without changing the value of the whole fraction.

When you multiply or divide any number by 1, the answer is the same number. This rule also goes for fractions, so

And as I discuss in Chapter
9
, when a fraction has the same number in both the numerator and the denominator, its value is 1. In other words, the fractions
are all equal to 1. Look what happens when you multiply the fraction
:

The net effect is that you've increased the terms of the original fraction by 2. But all you've done is multiply the fraction by 1, so the value of the fraction hasn't changed. The fraction
is equal to
.