The usage of denominator

"How will you explain to your students that when you add or subtract fractions you must have a common denominator but you do not need one with multiplication or division? In your explanation, make clear what a common denominator is and how to find it."

Step 1: I would give the definition of a common denominator which is defined as
Common denominator just means that the denominators in two (or more) fractions are common, or the same. example 2/5 +1/5

Step 2: I would explain to the student(s) how to find the common denominator. I will explain there are two ways to find the common denominator you can add you two bottom numbers(denominator) or you can list the multiples.  Example 1/2+2/5  2*5=10   or list multiples 2,4,6,8,10... 5, 10...

Step 3:  I would use a method of measurement to show them why the denominators have to be the same.  When it comes to adding or subracting(take-away) the bottom measurements have to be the same. For example I would draw a pizza graph.  First a pizza with three sides and only 1 slice left (1/3) + another with 6 sides and only 1 slice (1/6) you can't add the denominators because the are not the same.  Use one of the methods in step 2 to get your common denominator.   

When it comes to multiplication you just multiply across.  Changing the denominator will force the fraction to beome improper; which will change the entire problem.

 

Helpful Lesson!

The activity that really helped me was today, Monday March 21, when you put us in groups of 3's.  Fractions can be sometime complicated, but with a little reasurrance from your peers made it a bit easier.  Fractions can be hard, but they are very basic.  Even though we have been taught about fractions over and over since the 3rd grade, having a tutorial session is beneficial.  Being in groups helped my understanding better.  One group member may have a better understanding about a certain problem than another.  It's very helpful when you collabortate with your peers.  Now I have a better understanding of fractions.

Congratulations!

Good job, Erin.