2/19/2010
Multiplying and
Dividing
Fractions
two quarters are a half
a half of a quarter is an eighth
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2/19/2010
To multiply a fraction by a
whole number, multiply the
numerator and leave the
denominator as it is.
Simplify the answer as much
as possible.
two times a quarter is two quarters
two quarters is a half
two times three quarters is six quarters
six quarters are three halves
three halves are one and a half
To multiply a fraction by another
fraction
a half of a quarter is an eighth
a half of three quarters is three eighths
•multiply the numerators
together to find the new
numerator
•multiply the denominators
together to find the new
denominator.
Simplify the answer as much as
possible.
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2/19/2010
Dividing
is sometimes called the reciprocal of 2
and 2 the reciprocal of
They are multiplicative inverses.
If you multiply a number by its reciprocal, the answer will be 1
1
2
x
2=1
1
3
x
3=1
1
4
x
4=1
1
5
x
5=1
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2/19/2010
Multiplying by a number is the same as
dividing by its reciprocal
and dividing by a number is the same as
multiplying by its reciprocal
What is a half of a quarter?
an eighth
How many twos are there in a quarter?
an eighth (of two)
What are two quarters?
a half
How many halves are there in a quarter?
a half (of a half)
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2/19/2010
To divide one fraction by second fraction,
Turn the second fraction upside down and
then multiply them.
i.e. multiply the first number by the reciprocal of the second
Multiplication of fractions
expressed algebraically
Reciprocals are
multiplicative inverses.
a x 1/a = a/a = 1
a ÷ a = a/a = 1
Multiplying by a number’s
multiplicative inverse
gives the same answer as
dividing by the number
b x 1/a = b/a
b ÷ a = b/a
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