Math...er..

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Kit
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Math...er..

Post by Kit »

Fractions are weird and uncomprehendable for me! :crying:

Can someone explain to me how to work these things?





5/12 + (-3/20) =



-9 2/3 + 4 3/10=



-5 1/3 + 6 3/8=





How do you work them? How do you reduce?
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Gostridah
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Re: Math...er..

Post by Gostridah »

Let a/b and c/d be two fractions.



To calculate



a/b + c/d,



basically you do



(ad+bc)/bd



but numbers may get big if you do this (you can reduce later though), so instead if there are common divisors you can do



mcm[c,d]=x



Then



a/b+c/d= [(x/b )a+(d/x)c]/x



That looks ugly but it's easier when you're using actual numbers.
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Kit
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Re: Math...er..

Post by Kit »

a/b + c/d ?



Where did my teacher come up with the timesing something together at?
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Gostridah
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Re: Math...er..

Post by Gostridah »

a, b, c and d are variables. In other words, instead of saying



3/20+2/5, because that's one particular case, we say

a/b+c/d as a generalization.
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Re: Math...er..

Post by Spitfire »

Im gonna give this a shot, its been so long since Ive had to think like this.



OK. First, lets seeee...um... ok. You have to change the denominators so that they are the same. To do that you have to find the first common denominator, which is the first number that they can both be multiplied to. In this case, it is 60. So, you have to multiply the 12 by 5, and then you also have to multiply the 5 by 5 to make it equal. Thats how I got 25/60. Then you do the same for the bottom. But to get 20 to turn into 60, you have to multiply 20 by 3, and then you also have to multiply the numerator, -3, by 3 as well. Thats how I got -9/60.



5/12 = 25/60

+ -3/20 = -9/60

________ _____

16/60 To get 16/60 i just did 25 - (-9) to get 16 and the

denominator stays the same.



The last step is simplifying 16/60. All you have to do is find something that you can divide into both 16 and 60. The first number I think of is 2. So, I need to divide 2 into 16 getting me 8, and 2 into 60 gettting me 30.



16/2= 8 60/2=30



So, we end up with 8/30.



Since 8/30's can be simplified agian. We need to do that. I am going to use 2 agian. So I will divide 8 by 2 and 30 by 2 and get 4/15. Since 4/15 cant be simplified agian, that is the final answer.



A= 4/15





For the next problems you gotta do the same thing. There is just a whole number on the end that you have to subtract or add also. Somebody make sure that I did those right, cuz Im anquious to know if I even did it right because it has been a couple years since I have had to do fractions. If you read this and still need help with this one or the other 2, then just ask, ill keep watch.
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Re: Math...er..

Post by jess_617 »

Originally posted by Sammi17@Aug 16 2004, 09:27 PM

a/b + c/d ?



Where did my teacher come up with the timesing something together at?




Actually they are prolly wanting you to get a common denomenator. Which in this case would be 60, 30, and 24 respectively.



so the problems are reverted to





25/60 + (-9/60) =



-9 20/30 + 4 9/30=



-5 8/24 + 6 9/24=



after that its pretty simple, add and subtract. If you need any more help or if that didnt make sense IM SORRY!!! Ill try to help as much as I can. (also im pretty sure I did that right but if I didnt i apologize..today was my first day back lol)
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Re: Math...er..

Post by Kit »

ah ha!!! I gotededededed it. :D



5/12 + (-3/20) =



You cross multiply...5 x 20 = 100



and then -3 x 12 = -36



and then 20 x 12 = 240



so you subtract 36 from 100 which is 64.



So you are ended up with 64/240.



Then you reduce.... That's what my teacher said... I'm confused still but that's ok...I'm blonde and I deserve my blondeness :D Or did I still get that wrong? That's what it was on the paper!! :(



Spitfire, can you or anyone else like show me an example of what you just said? Pweeeez? Tank goo... :D
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Re: Math...er..

Post by Breathe_In_For_Luck7 »

All you have to do is find a least common denominator and add.



Ex.



5/12 + -3/20 =



5(5)/12(5) + -3(3)/20(3) =



25/60 + -9/60 =



16/60 = 4/15



The LCD was 60 and for the first fraction you had to multiply the top and bottom by 5 to get the bottom to be 60. For the second fraction you had to multiply the top and bottom by 3 to get the bottom to be 60.



Does this make sense? Or are you doing something completly different?
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Re: Math...er..

Post by Kit »

I don't know.. The thingy says "add and subtract ratios" or something to that affect and that's how he showed me how to do it on the paper...But I still don't get it...and I really don't get how to do any of which he did....Why can't you just add or subtract together the numbers like it says in the name?! That would me much simpler...but nooo....teachers have'ta make it difficult. :wacko: :angry:

I think I need to get out of this class and go back to Pre-Algebra...
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Re: Math...er..

Post by jess_617 »

Im sorry I didnt help much...its kinda difficult to explain on the computer. Itll prolly be more beneficial if you keep asking your teacher cuz none of us could explain it to your understanding. --------did that make sense?? o well lol
Hey everyone. Im around here alot so if anyone ever needs a chat feel free to PM me or add me on Yahoo, AIM, or MSN. I'll do my best to help. <3



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