Transcript Silly Monster

Fraction
Multiplication
and Division
Algebra Seminar
2012-2013
Fraction Multiplication
• Here are some fraction multiplication
examples.
• Can you tell how to multiply fraction from
these examples?
2 5 10
´ =
3 7 21
1 1 1
´ =
3 3 9
2 5 10
´ =
3 1
3
4 1
4
´ =
5 7
35
6
4
24
´
=
5 10
50
3 5 15
´
=
4 12 48
Multiplying Fractions
Together
1.) Multiply numerator by
numerator straight across the top
of the fractions.
2.) Multiply denominator by
denominator straight across the
bottom of the fractions.
2 5
10
´ =
3 1
3
Practice
1 5
´ =
3 8
5 5
´ =
8 8
2 4
´ =
3 5
4 2 2
´ ´ =
9 3 5
What if our fraction is in
the form of a mixed
number?
• Because of the order of operations, mixed
numbers cannot be multiplied.
• Change mixed numbers to improper fractions,
then multiply.
2
5
3 ´1 =
5
8
17 13 221
´ =
5 8
40
221
21
and
=5
40
40
Some to try.
1. Change any whole or mixed numbers to
improper fractions.
2. Multiply straight across.
3. Simplify answers.
2
2
1 ´7 =
5
3
2
´8 =
5
Fraction
Division
(Opposite of Multiplication)
Dividing two fractions is the
same thing as multiplying by
the reciprocal:
To find the reciprocal of a
fraction you flip the numerator and
denominator
3
4
becomes
4
3
Dividing Fractions Example
• Keep the first fraction the same.
• Change the division sign to
multiplication.
• Use the reciprocal of the second
fraction.
• Then multiply!
2 3 2 4 8
¸ = ´ =
5 4 5 3 15
1
¸2
4
1 2
¸
4 1
Tanner had a pizza and was
planning to eat one-fourth of the
pie. Jackson came over and
Tanner was nice enough to divide
his quarter in 2. How much of the
pizza did each person get?
1 1
´
4 2
1 1 1
´ =
4 2 8
Dividing Fractions with Mixed
Numbers
3
1
¸2
4
5
3 11
¸
4 5
3 5 15
´ =
4 11 44
• Remember! We
cannot multiply
mixed numbers.
• We must change
them to improper
fractions first!
Some More Practice
1 5
¸ =
3 2
2 5
1 ¸ =
5 6
5 3
¸ =
8 2
4
5
2 ¸1 =
7
2
Levi made fudge this weekend. He
wants to put 5 1/3 lbs of chocolate
into separate containers. Each
container holds 2/3 lb. How many
containers will he need?
1 2 16 3 8 1
5 ¸ = ´ = ´ = 8 containers
3 3 3 2 1 1