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October 12th, 2013, 05:01 AM  #1 
Senior Member Joined: Oct 2009 Posts: 895 Thanks: 1  probability could please check my answer ?
Hi An urn contains 6 red balls, 2 Green balls, 1 blue ball and 1 white ball. If a ball is drawn, find the probability of getting a red or white ball. My answer is [color=#0040FF] the total of balls are 10 so we can drawn that in 10C1 = 10 ways now probability of getting a red = 6C1 = 6 probability of getting a white = 1C1 = 1 required probability 6 X 1 / 10 = 0.6 [/color] Is my answer correct? 
October 12th, 2013, 05:20 AM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs  Re: probability could please check my answer ?
Since it is an OR, you want to add rather than multiply...

October 12th, 2013, 05:24 AM  #3 
Senior Member Joined: Oct 2009 Posts: 895 Thanks: 1  Re: probability could please check my answer ?
Thanks, I got it.

October 14th, 2013, 04:18 AM  #4 
Senior Member Joined: Oct 2013 From: Sydney Australia Posts: 126 Thanks: 0  Re: probability could please check my answer ?
Mark is right. Try to think about it logically. The combination formula is often very useful but it cannot replace basic understanding. P(event) = number of favourable events / total number of possible events number of favourable events is 7 because there are 7 balls that are red or white. Total number of events is 10 because there are 10 balls. Therefore P(red or white) = 7/10 

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