Given that P(A)=0.4, P(B)=0.5, and P(A and B) = 0.20, determine P (A|B)
M MGD New member Joined May 8, 2011 Messages 7 May 8, 2011 #1 Given that P(A)=0.4, P(B)=0.5, and P(A and B) = 0.20, determine P (A|B)
mmm4444bot Super Moderator Joined Oct 6, 2005 Messages 10,962 May 8, 2011 #2 What are your thoughts thus far?
M MGD New member Joined May 8, 2011 Messages 7 May 8, 2011 #3 P(A and B) = P(A) + P(B) - P(A|B) 0.20 = 0.4 + 0.5 - P(A|B) 0.20 = 0.9- P(A|B) 0.11 = -P(A|B) P(A|B)= -0.11 This is what I'm getting, but it doesn't seem correct. What am I missing, am I using the correct equation for this problem?
P(A and B) = P(A) + P(B) - P(A|B) 0.20 = 0.4 + 0.5 - P(A|B) 0.20 = 0.9- P(A|B) 0.11 = -P(A|B) P(A|B)= -0.11 This is what I'm getting, but it doesn't seem correct. What am I missing, am I using the correct equation for this problem?
G galactus Super Moderator Staff member Joined Sep 28, 2005 Messages 7,216 May 9, 2011 #4 It would appear you are mixing up P(A or B) and P(A|B) Try \(\displaystyle P(A|B)=\frac{P(A \;\ \text{and} \;\ B)}{P(B)}\)
It would appear you are mixing up P(A or B) and P(A|B) Try \(\displaystyle P(A|B)=\frac{P(A \;\ \text{and} \;\ B)}{P(B)}\)
