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October 13th, 2013, 03:18 PM  #1 
Senior Member Joined: Oct 2009 Posts: 895 Thanks: 1  questions in probability
Question 10 Rachel buys a new CD, on which is her favourite track, 8 other tracks she likes and 2 tracks that she does not like. She sets her CD player to play at random. What is the probability that the first track it plays is: (a) Rachel's favourite (b) a track that she likes (c) a track that she does not like [color=#800000]my answer a) 8/10 b) 8/10 C) 2/10[/color]  Q2 : Two fair dice are rolled at the same time. What is the probability that the total score is 1) 6 2) greater than 9 3) less than 7 4) that is an even number 
October 13th, 2013, 04:48 PM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,929 Thanks: 1124 Math Focus: Elementary mathematics and beyond  Re: questions in probability
Question 10: 1 + 8 + 2 = 11. Q2: 1) The number of possible outcomes is 36. Possible outcomes where both dies total 6 are (1, 5), (2, 4), (3, 3), (4, 2), (5, 1). The probability that the dice total 6 is 5/36. 2) 1/6. 3) 15/36. 4) 1/2. 
October 14th, 2013, 02:22 AM  #3 
Senior Member Joined: Oct 2009 Posts: 895 Thanks: 1  Re: questions in probability
Thanks, but in question number two, for 2, 3 and 4, can explain to me how you got that? 
October 14th, 2013, 04:07 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 20,467 Thanks: 2038 
It's just a matter of counting the possibilities. If, for example, the total score is greater than nine (i.e., 10 or more), there are six possibilities: (4,6), (5,5), (5,6), (6,4), (6,5), and (6,6). Hence the required probability is 6/36 = 1/6.

October 14th, 2013, 04:46 AM  #5 
Senior Member Joined: Oct 2013 From: Sydney Australia Posts: 126 Thanks: 0  Re: questions in probability
1a) 1/11 b) 9/11 c) 2/11 Q2 Draw a grid like this one The first die is horizontal the second is vertical. There are 36 possible combinations. Remember (1,2) is different from (2,1). Then you can just tick off the favourable boxes (I already put the additions in the boxes) a) 5/36, b) 6/36 c) 15/36, d) 18/36 just as Greg said. [attachment=0:1nxkdesg]2 dice grid.JPG[/attachment:1nxkdesg] 

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