# Stats/Probability problems

• June 10th 2008, 04:09 PM
bakeit1
Stats/Probability problems

Given P(A) = .3, P(B) = .5, P(A and B) = .2, find
a) P(A or B)

b) P(A|B)

c) P(A with bar on top)

A single card is drawn from a standard 52 card deck. Let A be the event "the card is a face card" and let B be the event "the card is a red card".
a) Find P(A) and P(B)

b) Find P(A|B)

c) Are A and B independent events? Explain why or why not.

I'm having troubles understanding these symbols etc. Can anyone somewhat explain the process I have to go through for each problem. Thanks.
• June 10th 2008, 08:54 PM
n00b3
what have you tried?

a) or usually means add the probabilities

b) P(a|b) = P(a)/P(b)

c) if an event has a probability of 13% chance of happening then it has an 87% chance of not happening. this is the complement.

Do you know the definition of a probability?
• June 11th 2008, 03:20 AM
Moo
Hello,

Quote:

Originally Posted by n00b3
what have you tried?

a) or usually means add the probabilities

b) P(a|b) = P(a)/P(b)

c) if an event has a probability of 13% chance of happening then it has an 87% chance of not happening. this is the complement.

Do you know the definition of a probability?

This is completely incorrect !!!
Your formulae are either false, either they do not fit in the situation.

a) $P(A \cup B)=P(A)+P(B)-P(A \cap B)$

where $\cup$ means "or" and $\cap$ means "and"

b) $P(A|B)=\frac{P(A \cap B)}{P(B)}$

c) $P(\bar A)=1-P(A)$

If you draw a diagram, most of the answers will fall out from it.