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#1 2013-07-13 12:23:51

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Multiplying fractions

Hey all i know this is really basic but i have hit a wall

(d / a+b) * (5a + 5b / 2d^2 + 2d)

i can get the answer but im not sure what im actually doing S:

i khow to multiply problem like (1/2) * (1/2) = 1/4 but what confuses me in this problem is the denominator a+b not sure how to multiply the other denominator with it.

My workings

(d / a+b) * (5a + 5b / 2d^2 + 2d)

i just divide by common factors first step
numerator 5a + 5b to 5 ( a+b)
then denominator 2d (d + 1)

then i just divided both numerator and denominator by common factors (a+b) and d
so i got the answer 5 / 2 (d + 1)

how would you guys solve it? sorry if my reasoning bit over the place, any chance you can show me your working so i can aware myself.

thank you.

Last edited by bronxsystem (2013-07-13 12:25:09)

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#2 2013-07-13 12:35:24

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

had another one that the method works but again not sure what im doing S:
( a + 3 / a - 5) * (2a - 10 / 3a + 9)

= (a + 3 / a - 5) * 2 ( a - 5) / 3 (a + 3)

then just divide numerator and denominators by common factors and i get 2/3

>< whats this called or what rule is it?

Last edited by bronxsystem (2013-07-13 12:42:23)

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#3 2013-07-13 16:00:00

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 90,678

Re: Multiplying fractions

Hi;

I would call it cancellation.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#4 2013-07-14 00:30:38

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

sorry those other 2 post had to much fluff a better question maybe is do you think the steps i take are acceptable?

eg

(3ab^2 / 4) * ( 12/ 18a^2)

just simply multiply numerators then denominators and then simplify

(36ab^2) / (72a^2)

then divide by common factor 36a

= b^2 / 2a

thats all it is right?






not sure why this way works i thought your meant to divide both numerator and denominator by same number S:

(3ab^2 / 4) * (12 / 18a^2)

first divide numerators by common factor 3

4ab^2

then divide denominators by common factor 2
2 (8a^2)

then divide both numerators and denominators by 2
(2ab^2 / 4a^2)

then divide by 2a
( b^2 / 2a)

Last edited by bronxsystem (2013-07-14 00:47:35)

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#5 2013-07-14 04:19:09

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 90,678

Re: Multiplying fractions

The first method is simpler.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#6 2013-07-14 04:22:53

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

roger thanks

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#7 2013-07-14 04:27:24

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 90,678

Re: Multiplying fractions

You are welcome.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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