September 30, 2014
Adding and Subtracting
Fractions
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Basic reminders:
Numerator (part)
Denominator (whole)
Example: I ate 2 of the 8 pieces of pie last night. So
I ate 2/8 (reduce it to 1/4) of the pie last night.
15 out of 29 students in my class are boys. So
15/29 of my class is male.
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We also need to remember how to change mixed
numbers into IMPROPER FRACTIONS. (Numerator is
bigger than denominator)
Remember "rock around the clock"?
Rock around the clock:
you multiply the numerator by the whole number, and then add
the numerator. The denominator stays the same.
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Can you "rock around the clock" and turn these mixed
numbers into improper fractions?
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Wait! Ms. Crane says...
Turning numbers into improper fractions
when adding/subtracting is not necessary, but
most of the time, this step will make the
process easier. If you don't turn them into
improper fractions, you run into the chance
off needing to regroup when adding or borrow
when subtracting. Yikes!
September 30, 2014
To add or subtract fractions, you need to find a
COMMON DENOMINATOR (this means both fractions
need to have the same bottom number)
You can't add or subtract until you are talking about the
same whole (denominator)
For example:
have common denominators!
September 30, 2014
But what happens when two fractions DON'T have a
common denominator??? You can do one of two things:
1) Find the Least Common Multiple (LCM). This is the
smallest number that BOTH denominators will go into.
2) Multiply both denominators together to get a common
denominator.
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here are some examples on how to find a common
denominator.
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Can you find the common denominator between the
following fractions?
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Okay, Great! Now that you know how to find the
common denominator, now you need to do the next step:
Change the numerator (multiply the numerator by the
same number that you multiplied the denominator)
Now, do that to the numerator!
Now you have two equivalent
(equal) fractions and you are ready
to add or subtract!!!
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Can you change the numerator? I've already helped you
out and found the common denominator for you...
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You are almost done! Remember the steps:
1) Change all mixed numbers to improper fractions
2) Find a common denominator
3) Change the numerator
4) Add or subtract the numerators, but the denominator
stays the same.
5) REDUCE WHEN YOU CAN!
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Let's Practice! Add or Subtract the following fractions:
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How can I make an improper fraction a mixed
number??
ex 1.) 9
ex 2.) 127
4
21
Now, you try...
ex 3.) 17
ex 4.) 11
15
10
September 30, 2014
Butterfly Fractions!
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Let's Add Negatives in the mix!!!!!! Yay!!
September 30, 2014