Transcript 3.4-3.5 Multiplying and Dividing Fractions

Multiplying and Dividing of Fractions
Section 3.4 Pages 123 – 129
Section 3.5 Pages 130 – 136
Quick Review
 When we multiply or divide two rational numbers we must
always be aware of the signs of the two numbers.
 Positive (x or
) positive = positive
 Positive (x or
) negative = negative
 Negative (x or
) positive = negative
 Negative (x or
) negative = positive
This would be a good chart to
copy down!
Reminder:

1
1
2
2
1
 
2
1
1
2
2
Multiplying Simple Fractions- Finding the
Product
 To multiply two simple fractions, complete the following
steps.
 1. Multiply the numerators.
 2. Multiply the denominators.
 3. Reduce the product.
 4. Identify the resulting sign on the question ( -/+)
 5. Reduce to lowest terms!!!
Example
3
5

2
3

3 2
53

6
15

2
5
Try ME:
 5 


 12 
 2
 
 9
 8 


 12 
 4
 
 7
Multiplying a Whole Number and a Fraction –
Finding the Product
 To multiply a whole number and a fraction,
complete the following steps.
 1. Convert the whole number to a fraction.
 2. Multiply the numerators.
 3. Multiply the denominators.
 4. Reduce the product.
 5. Identify the resulting sign ( -/+)
Try ME:
 3
2 
 4
7
8
  3 
What about mixed numbers?
 If a question contains a mixed number, simply
convert it to an improper fraction and…
 1. Multiply the numerators.
 2. Multiply the denominators.
 3. Reduce the product.
 4. Identify the resulting sign ( -/+)
Try ME:
2 
5

 6   1 

3 
6
2  5

 2   3 

5  9
Multiplying Rational Numbers in Decimal form
 1. Predict the sign ( +/-)
 2. Using compatible numbers to solve the
question
 3. Place the correct number of decimal places
into your product
Try ME:
(-0.4)( -0.7)
(0.5)(- 2.4)
Dividing Simple Fractions- Find the
Quotient
 To divide one fraction by a second fraction,
convert the problem to multiplication and
multiply the two fractions.
 1. Change the second fraction to its reciprocal
 2. Multiply the numerators.
 3. Multiply the denominators.
 4. Reduce the quotient.
 5. Identify the sign result of the question (+/-)
What is a reciprocal?
 Reciprocal  The numerator and denominator
are switched.
 OR the fun way to remember it…
What is a reciprocal?
4
5
5
4
Reciprocal:
A fraction doing
a handstand!
Try ME:
 3  6 
    
 2  7
 7  9
    
 9  4
Dividing Fractions with Mixed
Numbers
 To divide a fraction by a whole number:
 1. Convert the mixed number to an improper
fraction.
 2. Change the second fraction to the reciprocal
 3. Multiply the numerators.
 4. Multiply the denominators.
 5. Reduce the quotient.
 6. Identify the sign result of the question (+/-)
Just like in multiplication, convert all
mixed numbers to improper fractions
before dividing!
Try ME:
3 
5

 3    2 

5 
6
1 
9 

 6    2




2
10 
 Pg.127-129 1,2,7,9,11,12,14,16
 Pg.134-136 3,9,12,14, 21
Homework
 See the Worksheets that accompany these sections.