mohican Posted June 16, 2005 Share Posted June 16, 2005 A bag contains 6 balls, 2 red, 2 blue and 2 green. What is the probability of NOT selecting blue balls in 2 successive draws Is it 4/6 * 3/5 = 12/30 = 2/5 ? Quote Link to comment Share on other sites More sharing options...
ish Posted June 16, 2005 Share Posted June 16, 2005 The way I see it: The prob of selecting two blue balls in 2 consec draws is (2/6)*(1/5) =1/15 Thus the prob of not selecting 2 blue balls is 14/15 Do you have the OA? Quote Link to comment Share on other sites More sharing options...
mxr55820 Posted June 16, 2005 Share Posted June 16, 2005 My solution: total combination : 6c2 = 15 total comnbination with red and green ball = 4c2 = 6 P(of selecting red and green ball) = P(of NOT selecting any blue ball) = 6/15 = 2/5 Quote Link to comment Share on other sites More sharing options...
mohican Posted June 16, 2005 Author Share Posted June 16, 2005 No, I do not have an OA, I am trying to get some of my basics right. I thing ARJMAN can help here Quote Link to comment Share on other sites More sharing options...
arjmen Posted June 16, 2005 Share Posted June 16, 2005 A bag contains 6 balls, 2 red, 2 blue and 2 green. What is the probability of NOT selecting blue balls in 2 successive draws The wording on such questions need to be scrutinized. If the question asks for the probability of neither draw turning up a ball (i.e. no blue balls at all) then this is akin to drawing the 2 balls from a group of balls that does not have any blue ones. Total ways of drawing 2 balls from 6 = 6C2 = 15 Ways to draw 2 balls from 4 (6 balls minus the 2 blue balls) = 4C2 = 6 P(not drawing a blue ball in either draw) = 6/15 = 2/5 ----------------------------------------------------------------------------------------------------- If the question asks for the probability of the draws not turning up 2 blue balls (i.e one blue ball drawn is allowed, but not two) then, P(favourable event) = 1 - P (both balls blue) = 1 - 2C2/6C2 = 1 - 1/15 = 14/15 ----------------------------------------------------------------------------------------------------- I reckon the former case is being asked for here and so the correct response should be 2/5 Quote Link to comment Share on other sites More sharing options...
Priyadarshi Posted June 16, 2005 Share Posted June 16, 2005 Well the solution is : 4/6 *3/5 ( slecting from balls other than blue ) = 2/5 The mistake you have done ish is you have first found the prob of selceting two blue balls and then subtracted it from 1 , which mean you have found the prob of not getting two successive blue balls , but IT CAN BE ONE BLUE BALL IN ONE OF THE DRAWS or NO BLUE BALL. WHICH MEANS WHAT YOU FOUND OUT WAS : if the first one was a blue and then non blue or first non blue then blue or both non blue : 2/6*4/5 +4/6 *2/5 + 2/5 ( we have already found this ) = 14/ 15 .. MATCHES WITH WHAT YOU FOUND !! sorry for the use of caps just to highlight the main point of the concept. Quote Link to comment Share on other sites More sharing options...
mohican Posted June 16, 2005 Author Share Posted June 16, 2005 Thanks a lot for explaining , arjmen Quote Link to comment Share on other sites More sharing options...
ish Posted June 17, 2005 Share Posted June 17, 2005 Well the solution is : 4/6 *3/5 ( slecting from balls other than blue ) = 2/5 The mistake you have done ish is you have first found the prob of selceting two blue balls and then subtracted it from 1 , which mean you have found the prob of not getting two successive blue balls , but IT CAN BE ONE BLUE BALL IN ONE OF THE DRAWS or NO BLUE BALL. WHICH MEANS WHAT YOU FOUND OUT WAS : if the first one was a blue and then non blue or first non blue then blue or both non blue : 2/6*4/5 +4/6 *2/5 + 2/5 ( we have already found this ) = 14/ 15 .. MATCHES WITH WHAT YOU FOUND !! sorry for the use of caps just to highlight the main point of the concept. Thats very helpful Priyadarshi. thanks.:) Quote Link to comment Share on other sites More sharing options...
chintz Posted June 17, 2005 Share Posted June 17, 2005 Thanks a lot for explaining , arjmen Even i thought like ish. Quote Link to comment Share on other sites More sharing options...
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