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Monday, May 11, 2009
Adding and Subtracting Fractions
To add fractions, you have to find the common the denominator. After finding out the common denominator, you have to figure out the numerator; you either cross multiply (the easiest way) or, find out how many times the first denominator goes into the common denominator, then multiply that number by the first fraction.
Example: 5/7 + 1/2

My next example is 5/9 + 1/3.

Now I'm going to give an example of subtracting fractions.

This question contains mixed numbers. All you have to do is change that mixed number into an improper fraction. To change it into improper, multiply the whole number by the denominator and add the numerator.

Multiplying Fractions 
To multiply fractions, you simply have to multiply the numerators together and the denominators together.

My second example for multiplying is 4 2/5 x 1/2.
This question also contains a mixed number. Just like the subtracting question, you have to convert it into a improper fraction. Then, to get the answer you have to see how many times does 10 goes into 22. 

Dividing Fractions
To divide fractions, you have to see how many times groups of that number goes into the other number (How many groups of __ goes into __?) An example is 3/4 / 1/3.
For this question, I decided to use a ratio table along with the fraction's reciprocal. The reciprocal is when you switch the fraction around and get a product of 1.

Word Problem

To get the answer, divide how many scoops of flour we have by how many scoops it takes to make one cake (use the improper fraction). Then multiply both fraction by how many scoop it takes to make one cake's reciprocal.

It was sunny in Winnipeg for 3 hours and 30 minutes.
To get the answer, multiply how many hours of daylight by the fraction of how long it was sunny.


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