how do you subtract fractions with unlike denominators?
DESCRIPTION
How do you subtract fractions with unlike denominators?. For example, what is - ?. -. In this lesson you will learn how to subtract fractions with unlike denominators by using fraction bars. We know that fractions need to have the same denominator to subtract them. . - PowerPoint PPT PresentationTRANSCRIPT
How do you subtract fractions with unlike denominators?
For example, what is - ?
-
In this lesson you will learn how to subtract fractions with unlike denominators
by using fraction bars.
Let’s Review
We know that fractions need to have the same denominator to subtract them.
I remember my teacher called this a common denominator.
I can use equivalent fractions to
make common denominators.
Let’s Review
We know that equivalent fractions show equal amounts.
= = = = =
This could go on forever!
How do I decide which equivalent fraction to use?
Let’s Review
When one denominator is a divisor of the other, only one fraction has to be changed.
-
-
2 is a divisor of 8 so I will make an
equivalent fraction for .
=
Let’s Review
When both denominators are multiples of 10, only one fraction has to be changed.
- =51100
I know that is equivalent to
70100
19100
A Common Misunderstanding
Students begin to subtract without forming a common denominator.
-
-≠
≠
Core LessonWhat is - ?
-
One denominator is not a divisor of
the other.
Neither denominator is a multiple of 10.
How do I decide which equivalent
fractions to form?
I can multiply any number by 1 without changing its value.
Core Lesson
-
+
Look at the denominator of the other fraction.
x Divide each part of the whole by 3
Multiply the pieces by 3=
=
Core Lesson
-
+
Look at the denominator of the other fraction.
x Divide each part of the whole by 2
Multiply the pieces by 2=
= -
=
Core Lesson
-
=
=
Now I can subtract.
= -
Core LessonSammy says that - = , but
Trevan says it subtracts to leave .
It’s . It’s
Core Lesson
What is - ?
-
One denominator is
not a multiple of the other.
Neither denominator is a multiple of 10.
How do I decide which equivalent
fractions to form?
I can multiply any number by 1 without changing its value.
Core Lesson
-
Look at the denominator of the other fraction.
x Divide each part of the
whole by 3
Multiply the pieces by 3=
- = 2
5
Core Lesson
Look at the denominator of the other fraction.
x Divide each part of the whole by 5
Multiply the pieces by 5= = -
-13
=
-
Core Lesson
Now I can subtract.
-
=
= -
115 =
Core Lesson
Trevan was correct because - =
It’s . Now I see it!
In this lesson you have learned how to subtract fractions with
unlike denominators by using fraction bars.