Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**anyarules****Member**- Registered: 2005-07-24
- Posts: 29

Hi can u plz answer this question. I find it ...well it makes me go

********************************************************************************Why do you need to turn the second fraction upside down when you are dividing a fraction by another fraction?

e.g 4 1

_ divided by _

9 2

Why do u make 1/2 into 2/1?

********************************************************************************Thats it...

(don't you just hate simple questions that u cant get the answer out of?)

{}

Offline

**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Consider a / b. This could be written as a * 1/b. Now let a = 3/2 and b = 1/2. (3/2) / (1/2)

Take the 1/2. What we want is 1 / (1/2), which would be 1 / b. Multiply this by 2/2 (which is multiplying it by 1, thus not changing the value). You get (1 * 2) / ( (1/2)*2 ) = 2 / 1

So 1 / b = 2 / 1. a * 1 / b = 3/2 * 2 / 1.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

Offline

**RickyOswaldIOW****Member**- Registered: 2005-11-18
- Posts: 212

I think you are right about flipping one of the fractions, only you need to then multiply each side (not divide)

(4/9) / (1/2) = (4/9) * (2/1)

4 * 2 = 8

-----------

9 * 1 = 9

But then again, I'm pretty terrible with algebra

Aloha Nui means Goodbye.

Offline

**VR Hawks****Member**- Registered: 2005-11-26
- Posts: 401

I don't really know, but let's explain it like this:

------------------------------------------------

4 divided by 2 also equals 4 times 1/2 (2 turned upside down).

4/2 = 4 x 1/2

------------------------------------------------

So, 4/9 divided by 1/2 could also equal 4/9 times 2[/1] (1/2 turned upside down).

4/9 // 1/2 = 4/9 x 2[/1]

------------------------------------------------

Get it?

**Name ::** Vincent Raider Hawks**Gender ::** Male**Birth Date ::** July 4 , 1970

Offline

**yonski****Member**- Registered: 2005-12-14
- Posts: 67

Rather than struggle to do it in here, i've knocked up a basic proof thingy. I couldn't figure out how to post it as an image, so here's a link to the image instead:

http://img64.imageshack.us/img64/8128/f … of16xb.png

Hope that helps.

Student: "What's a corollary?"

Lecturer: "What's a corollary? It's like when a theorem has a child. And names it corollary."

Offline

**anyarules****Member**- Registered: 2005-07-24
- Posts: 29

Can you guys make it a bit more simpler?

Offline

**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,603

Dividing by a number is the same as multiplying by 1/number

Example: 5 divided by 7 = 5/7, is the same as 5 multiplied by 1/7 = 5×1/7 = 5/7

So when dividing a fraction it is easier to multiply by 1/fraction.

Read Dividing Fractions

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

Offline

**RickyOswaldIOW****Member**- Registered: 2005-11-18
- Posts: 212

**Easy Method!!!**

Take the 2 fractions you wish to divide. Flip one of them over. Then multiply the 2 new fractions together (multiply the top numbers, then multiply the bottom numbers). That will give you the correct answer.

4 1

_ Divided by _

9 2

becomes

4 2

_ Multiplied by _ <----- *This part has been flipped over*

9 1

and thus

4 * 2 = 8

9 * 1 = 9

So your answer would be 8/9

8

_

9

*Last edited by rickyoswaldiow (2006-01-15 21:39:31)*

Aloha Nui means Goodbye.

Offline

**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

rickyoswaldiow, (s)he's asking:

Why do u make 1/2 into 2/1?

Not just how. I guess one reason why is because it's hard to divide fractions, but it's easy to multiply them. I don't think that one was ever said.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

Offline

**RickyOswaldIOW****Member**- Registered: 2005-11-18
- Posts: 212

I think the problem was, anya was flipping one fraction but still dividing them. I was emphasising that you need to multiply it once flipped. Like you say, it's easier to multiply it that way

Aloha Nui means Goodbye.

Offline

**John E. Franklin****Member**- Registered: 2005-08-29
- Posts: 3,588

4/9 divided by 1/2

4 divided by 1 is 4 on top.

9 divided by 2 is 4 and a half on bottom.

Hence 40/45

**igloo** **myrtilles** **fourmis**

Offline

**anyarules****Member**- Registered: 2005-07-24
- Posts: 29

I still don't get it...........

Offline

**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,092

When one rational number is divided by the other, the reciprocal of the second is multiplied by the first.

Examples:-

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Offline

**krassi_holmz****Real Member**- Registered: 2005-12-02
- Posts: 1,905

we can represent fractions ae 2d points:

Let a/b-->{a,b}.

Then we define the following functions:

sum({a,b},{c,d})={ad+cb,bd};

product({a,b},{c,d})={ac,bd};

{a,{b,c}}={ac,b};

{{a,b},c}={a,bc};

IPBLE: Increasing Performance By Lowering Expectations.

Offline

Pages: **1**