Solution to

Frame 2-29.

Instead of looking for the biggest number that divides into both the

numerator and denominator evenly (called the "largest common

denominator"), you can divide by **prime **numbers. A prime number is a

4

2

=

number that cannot be divided by any whole number other than itself and

10

5

1 without leaving a remainder. Prime numbers include 2, 3, 5, 7, 11, 13,

17, 19, 23, 29, 31, and so on. Begin with "2." If "2" divides into both the

3

1

=

numerator and denominator evenly (no remainder), then reduce the

6

2

fraction by two. Take the new fraction and try to reduce the new

numerator and denominator by "2" again. Continue until the fraction can

6

1

=

no longer be reduced by 2. Then do the same with the next prime

24

4

number ("3"). Continue until there is no whole number (other than 1) that

will divide into both the numerator and the denominator evenly. For

7x4

28

7

=

=

example:

8x1

8

2

2

2

2

3

48

48

24 ; 24

12 ; 12

6 ; 6

2

=

=

=

=

=

72 2

36 2

18 2

93

72

36

18

9

3

NOTE: On 6/9, 2 will divide evenly into 6 but not into 9. Therefore, you

go to the next prime number.

A variation is to break both the numerator and the denominator down into

prime factors (prime numbers that yield the original number when

multiplied). If the same factor appears in both the numerator and

denominator, mark it out. Mark out factors one at a time. [For example,

if you have "2" as a factor 3 times in the numerator but only twice in the

denominator, you can only mark out two of the "2's" in the numerator.]

When you are finished, multiple the remaining factors to obtain the

reduced fraction. For example:

48

2x2x2x2x3

2x2x2x2x3

2

=

=

=

72

2x2x2x3x3

2x2x2x3x3

3

Reduce 200/375 by this method.

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MD0900

2-13

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