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April 4th, 2014, 02:18 AM   #1
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Cancelling factors.

Hi, In the textbook Introduction to probability, by John E. Freund, there is one section that is not explained very well by the author. He shows two formulas where some factors is canceled, and the only note he gives is "Cancelling as many factors as possible before performing any multiplications, we would thus have obtained....".
The attached image shows my recreation of the formulas as they are printed in the textbook.
1. Could someone please explain the logic behind the cancelations in the attached formula?

2. In the second formula, why is number 12 not cancelled? Is there a typo?
EDIT ( ItÂ´s obviously a typo in the textbook, thanks MarkFL for pointing that out)
Thanks for any help!
Attached Images
 cancelfactors 2.jpg (16.8 KB, 13 views)

Last edited by zengjinlian; April 4th, 2014 at 02:36 AM. Reason: picture typo

 April 4th, 2014, 02:29 AM #2 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 461 Math Focus: Calculus/ODEs Yes, the 12 should be cancelled in the computation.
April 4th, 2014, 02:35 PM   #3
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Quote:
 Originally Posted by zengjinlian Could someone please explain the logic behind the cancelations in the attached formula?
5 x 4 x 2 = 40
80 = 40 x 2

So we have divided top and bottom of the quotient by 40.

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