October 09, 2014
Adding and Subtracting
Fractions
October 09, 2014
Intro Activity:
Brainstorm with your group and write down
everything you can remember about fractions!
Have someone write your ideas down.
October 09, 2014
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.
October 09, 2014
Remember how to add and subtract fractions?
October 09, 2014
Today, we are going to work in partners.
Everybody stand up (take your stuff) and go
to the back of the room. I will tell you who
your partner is and where to sit.
October 09, 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!
October 09, 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.
October 09, 2014
here are some examples on how to find a common
denominator.
October 09, 2014
Can you find the common denominator between the
following fractions?
October 09, 2014
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!!!
October 09, 2014
Can you change the numerator? I've already helped you
out and found the common denominator for you...
October 09, 2014
To practice, let's use the examples from
above, and change their numerators.
October 09, 2014
October 09, 2014
October 09, 2014
Now, we can add/subtract!
**Remember add/subtract numerator. Denominator stays the
same. Don't forget to reduce if needed!
1.) Add.
3.) Subtract.
2.) Subtract.
4.) Add.
October 09, 2014
You are almost done! Remember the steps:
1) Find a common denominator
2) Change the numerator
3) Add or subtract the numerators, but the denominator
stays the same.
4) REDUCE WHEN YOU CAN!
October 09, 2014
Butterfly Fractions!
October 09, 2014