Transcript Dividing Rational Numbers

Dividing Rational Numbers
Pre-Algebra
Vocabulary
Rational Number: Any number that can be
written as a fraction.
Reciprocal/Multiplicative Inverse:
Two numbers whose product is 1.
(Switch the numerator and the
denominator.)
Example:
5 15

24 36
In order to divide fractions, just
remember Kentucky Chicken Fried.
K – Keep
 the first fraction the same
C – Change the division to multiplication
F – Flip the second fraction (take the
reciprocal)
We keep the first fraction in our problem.
We change the division to multiplication.
We flip the second fraction by taking the
reciprocal .
5 15

24 36
5
36

24 15


Now we multiply.
1 5 36 3
3
1



6
2
2 24 15 3
Since 5 and 15 share a factor of 5, we may
 our problem.
factorout 5 from
Since 24 and 36 
share afactor of 12, we may
problem.


 our
factor
out 12 from
We multiply across horizontally.
Finally, we simplify if necessary.



1
4
Example #2: 2  5
3
9
This time we must change our mixed
numbers into improper fractions!
 1
2
 3
4
5
9
First we multiply 3 and 2 which yields 6.
Then we add 1 to 6 and get 7.
First we multiply 9 and 5 which yields 45.
Then we add 4 to 45 and get 49.
Our new problem is now:
7 49

3
9
We now use Keep, Change, Flip (KCF)
to divide.
K
1 7
1 3


We factor.
C

F

9 3
49 7

Andfinally, we 
multiply.
 

3

7