Ordering Improper FractionsDate: 10/12/2002 at 16:39:40 From: Raphie Subject: Ordering improper fractions Dr. Math, I have tried to figure out how to explain ordering improper fractions. But I don't even understand how to do it in the first place, meaning I won't be able to explain it! Please tell me how to do this so I can finish my math homework. Sincerely, Raphie Date: 10/12/2002 at 17:01:32 From: Doctor Sarah Subject: Re: Ordering improper fractions Hi Raphie - thanks for writing to Dr. Math. Putting improper fractions in order is easier than working with mixed numbers. Just give them a common denominator. For example, put the following improper fractions in order: 5/2 6/1 8/3 11/6 The common denominator is 6: 5/2 = 15/6 6/1 = 36/6 8/3 = 16/6 11/6 = 11/6 So in order, least to greatest: 11/6 = 11/6 5/2 = 15/6 8/3 = 16/6 6/1 = 36/6 Does this help? - Doctor Sarah, The Math Forum http://mathforum.org/dr.math/ Date: 10/12/2002 at 17:10:00 From: Doctor Ian Subject: Re: Ordering improper fractions Hi Raphie, Suppose you have to order some integers, like 5, 2, 1, 9, 3 At some point, you need to compare pairs of numbers, e.g., 5 < 9 right? Now, that's easy for integers, and harder for fractions, but there is one technique that works for both. That is this: Divide one number by the other; if you end up with something less than 1, the first number is smaller; if you end up with something greater than 1, the first number is larger. (If you end up with exactly 1, the numbers are equal.) With integers, it looks like 5/9 is less than 1, so 5 < 9 7/4 is greater than 1, so 7 > 4 Now, what if we have two fractions, like 1/3 and 2/5? We can do the same thing: 1/3 1 5 5 ----- = - * - = - 2/5 3 2 6 which is less than 1, so 1/3 is smaller than 2/5. For fun, let's try it the other way: 2/5 2 3 6 ----- = - * - = - 1/3 5 1 5 which is greater than 1, so 2/5 is larger than 1/3. (That's good, because if we'd arrived at a different answer, we'd be in trouble.) Let's try the fractions 2/3 and 14/21: 2/3 2 21 42 ------- = - * -- = -- 14/21 3 14 42 which is equal to 1... so 2/3 and 14/21 have the same value! Does this make sense? Note that this works for ANY numbers - integers, fractions, and improper fractions too. So if I have two improper fractions like 21/15 and 39/24, then 21/15 21 24 ------- = -- * -- = ... 39/24 15 39 Now, before I multiply all these out, I want to see if I can cancel some factors, because that will make my life easier. I know that 21 and 39 are both divisible by 3, so I can divide both of them by 3 to get 21/15 7 24 ------- = -- * -- = ... 39/24 15 13 Also, 15 and 24 are both divisible by 3: 21/15 7 8 ------- = -- * -- = ... 39/24 5 13 I don't see any more cancellations I can do, so I'll go ahead and multiply: 21/15 7 8 56 ------- = -- * -- = -- 39/24 5 13 65 which is less than 1, so I know that 21/15 is less than 39/24. Now, with improper fractions, there is something else you can try, which is changing them into mixed numbers. For 21/15 and 39/24, this won't help much, because we get 1 6/15 and 1 15/24, and we still have to compare the fractional parts. But if you have improper fractions like 39/24 and 105/41, then converting to mixed numbers, 39/24 = 1 15/24 105/41 = 2 23/41 you can see right away that one plus a proper fraction is smaller than two plus a proper fraction, regardless of what the fractions are. Does that make sense? Finally, sometimes you might be able to get all the improper fractions to have the same denominator. For example, to order 8/3, 14/12, 21/16 you might notice that 48 is divisible by all these denominators, so you can convert to the equivalent fractions 8/3 * 16/16 = 128/48 14/12 * 4/4 = 56/48 21/16 * 3/3 = 63/48 and now you can just forget about the denominators, so it's just like trying to order 63, 64 and 128. Does this help? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/