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April 4th, 2014, 02:18 AM  #1 
Member Joined: Jun 2012 Posts: 91 Thanks: 0  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! 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: 12,170 Thanks: 472 Math Focus: Calculus/ODEs 
Yes, the 12 should be cancelled in the computation.

April 4th, 2014, 02:35 PM  #3 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,313 Thanks: 2447 Math Focus: Mainly analysis and algebra  

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