Subtracting Mixed Numbers By Counting OnDate: 06/01/98 at 17:48:01 From: james owen Subject: Subtracting mixed numbers ?? + 1 and 3 fourths = 4 and 5 twelfths I tried inverse operations and it doesn't work. Date: 06/01/98 at 18:07:41 From: Doctor Pat Subject: Re: Subtracting mixed numbers James, Let's picture the problem in our minds. The question is, how much must we add to 1 and 3 fourths to make something 4 and 5 twelfths long. Let's add a little at a time until we get there. How much would we have to add to make it to 2 units? One fourth. So now we have a length of 2 units and we still need to make it longer. Can you think how much to add to get out to 4? Of course you could, and it is 2 more units. Now we just need to add enough to get from 4 out to 4 and 5 twelfths, and that seems easy, too. We need to add five twelfths. So in all we need to add 1 fourth + 2 wholes + 5 twelfths. Since 1 fourth is the same as 3 twelfths we can rewrite that as: 3 twelfths + 2 wholes + 5 twelfths = 2 wholes and 8 twelfths If you know how to simplify fractions you can make that 2 and 2 thirds. This method is called "counting on" and is a good way to think about doing fraction problems. Sometimes a picture of a number line will help, so I've drawn the kind of picture I would use below: |___________|___________|___________|___________|_____ 0 1 2 3 4 4 + 5/12 |___________|_________ 0 1 1 + 3/4 |_______________________________| this is what we need to find |1/4| |_______2 units________| |5/12| Can you see how we can put the pieces together? I hope this helps you figure out how to do mixed number subtraction by adding on. Good luck, -Doctor Pat, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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