My Math Forum Probability

 August 9th, 2011, 01:48 AM #1 Newbie   Joined: May 2009 Posts: 7 Thanks: 0 Probability P(A)=0.30 P(B)=0.45 P(A?B)=0.75 P(A?B)=P(A?B)/(P(B))=0.75/0.45=1.667 P(B?A)=P(A?B)/(P(A))=0.75/0.30=2.5 P(A?B)=P(A)+P(B)-P(A?B)=0.30+0.45-0.75=0 P(A)=0.30 P(B)=0.45 and A and B are independent P(A?B)=P(A)=0.30 P(B?A)=P(B)=0.45 P(A?B)=P(A)×P(B)=0.30×0.45=0.135 P(A?B)=P(A)+P(B)-P(A?B)=0.30+0.45-0.75=0 P(A)=0.30 P(B)=0.45 and A and B are mutually exclusive P(A?B)=0 P(B?A)=0 P(A?B)=0 P(A?B)=P(A)+P(B)-P(A?B)=0.30+0.45-0=0.75 Can anyone confirm that all my answer are correct? I was having some difficulty but i've attempted all the questions to show that i've had a go.
 August 9th, 2011, 01:17 PM #2 Global Moderator   Joined: May 2007 Posts: 6,820 Thanks: 722 Re: Probability The first one is absolutely incorrect. P(A)=0.30 P(B)=0.45 P(A?B)=0.75 - can't be. The probability of an intersection is at most the probability of the smaller. The second has an error at the end. P(A?B)=P(A)+P(B)-P(A?B)=0.30+0.45-0.75=0 - you used the wrong value for the probability of intersection. The line before you had it 0.135 (correct value). The third is correct.

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