Tuesday, January 22, 2013

Subtracting Fractions

Since addition and subtraction are inverse operations, subtracting Fractions is similar to adding fractions in that you must have the same size pieces.  The video from www.khanacademy.org has a useful model to show you why simplifying is important.

Be careful when subtracting mixed numbers.  You may need to borrow from the whole.  If you borrow one whole you need to convert that to a fraction to add to the fraction portion of the mixed number.  You have not changed the value but have renamed the mixed number in a way that allows you to compute.  In the second example pictured below, the one whole was converted into 27/27 to because it needed to be added to 3/27.

The video below shows the algorithm step by step.

No comments:

Post a Comment