Observe a very important property of a fraction that has been reduced to lowest terms. The
only whole number that divides
both the numerator and denominator without a remainder is the number 1. When 1 is the only whole number that divides two whole numbers, the two whole numbers are said to be
relatively prime .
Relatively prime
A fraction is reduced to lowest terms if its numerator and denominator are
relatively prime .
Methods of reducing fractions to lowest terms
Method 1: dividing out common primes
- Write the numerator and denominator as a product of primes.
- Divide the numerator and denominator by each of the common prime factors. We often indicate this division by drawing a slanted line through each divided out factor. This process is also called
cancelling common factors .
- The product of the remaining factors in the numerator and the product of remaining factors of the denominator are relatively prime, and this fraction is reduced to lowest terms.
Sample set b
Reduce each fraction to lowest terms.
1 and 3 are relatively prime.
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4 and 5 are relatively prime.
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7 and 13 are relatively prime (and also truly prime)
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15 and 16 are relatively prime.
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No common prime factors, so 8 and 15 are relatively prime.
The fraction
is reduced to lowest terms.
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Practice set b
Reduce each fraction to lowest terms.
Method 2: dividing out common factors
- Mentally divide the numerator and the denominator by a factor that is common to each. Write the quotient above the original number.
- Continue this process until the numerator and denominator are relatively prime.
Sample set c
Reduce each fraction to lowest terms.
. 5 divides into both 25 and 30.
5 and 6 are relatively prime.
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. Both numbers are even so we can divide by 2.
Now, both 9 and 12 are divisible by 3.
3 and 4 are relatively prime.
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. 7 and 5 are relatively prime.
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. 3 and 8 are relatively prime.
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Practice set c
Reduce each fraction to lowest terms.
Raising fractions to higher terms
Equally as important as reducing fractions is raising fractions to higher terms. Raising a fraction to higher terms is the process of constructing an equivalent fraction that has higher values in the numerator and denominator than the original fraction.
The fractions
and
are equivalent, that is,
. Notice also,
Notice that
and that
. We are not changing the value of
.
From these observations we can suggest the following method for converting one fraction to an equivalent fraction that has higher values in the numerator and denominator. This method is called
raising a fraction to higher terms .
Raising a fraction to higher terms
A fraction can be raised to an equivalent fraction that has higher terms in the numerator and denominator by multiplying both the numerator and denominator by the same nonzero whole number.