Given P(A) = .4, P(B) = .5, and P(A or B) = .7,

a)find P(A and B)

b)find P(A/B)

c)find P(B/A)

d)are A and B independent? Why, or why not?

Had trouble with this of probability question on my exam..any help is much appreciated...Thanks!

Printable View

- Nov 22nd 2009, 08:05 AMlisa1984wilsonProbabiltiy:
Given P(A) = .4, P(B) = .5, and P(A or B) = .7,

a)find P(A and B)

b)find P(A/B)

c)find P(B/A)

d)are A and B independent? Why, or why not?

Had trouble with this of probability question on my exam..any help is much appreciated...Thanks!

- Nov 22nd 2009, 08:54 AMFocus
- Nov 22nd 2009, 08:56 AMCaptainBlack
Draw a Venn diagram, and use it to determine P(A and B) (that is A intersection B)

That should allow you to answer a), b) and c). For d) you need to determine if:

P(A and B)=P(A)P(B)

(when A and B will be independednt and not if this does not hold) and you have sufficient data to do so.

CB - Nov 22nd 2009, 09:43 AMmatheagle

from that link....

Two events*A*and*B*are**independent**if and only if Pr(*A*∩*B*) = Pr(*A*)Pr(*B*). - Nov 22nd 2009, 03:46 PMlisa1984wilson
Given P(A) = .4, P(B) = .5, and P(A or B) = .7,

a)find P(A and B) P(A and B)=P(A)+P(B)-P(A or B)=.4+.5-.7=.2

b)find P(A/B) P(A/B)=P(A or B)/P(B)=.7/.5=1.4

c)find P(B/A) P(B/A)=P(A or B)/P(A)=.7/.4=1.75

d)are A and B independent? Why, or why not?

Not independent because P(A or B) does not equal P(A)P(B)

- Nov 22nd 2009, 03:49 PMmatheagle
- Nov 22nd 2009, 03:54 PMlisa1984wilson
I'm sorry...I'm just having trouble with this one, I did get this wrong on my exam. I'm just trying to get it right so can practice it before my next exam.

- Nov 22nd 2009, 06:26 PMmatheagle