Toss a die twice and take the sums. Let A be the event that the sum of the two numbers rolled is 6. Let B be the event that you roll a 6 on the first roll. Is there a negative relationship between A and B?
I believe there is, but I'd like to have my working checked out.
[math]AB = \emptyset[/math] and therefore [math]P(AB)=0[/math].
[math]A = \{(1,5), (2,4), (3,3), (4,2), (1,5)\}[/math] and therefore [math]P(A)=\frac{5}{36}[/math]
[math]B = \{(6,1), (6,2), (6,3), (6,4), (6,5), (6,6)\}[/math] and therefore [math]P(B)=\frac{6}{36}=\frac{1}{6}[/math]
[math]P(AB) < P(A)P(B)[/math]
[math]\frac{P(AB)}{P(B)}=P(A)[/math]
[math]P(A|B) < P(A)[/math]