Any Statisticians in here?

Ricochet J · 31 May 2007 at 15:45

I need help!

If A and B are two events and P(A)=0.6 and P(B)=0.3 and P(AuB)=0.8 find:
a) P(AnB)
b) P(A'nB)
c) P(AnB')
d) P(A'nB')
e) P(AuB')
f) P(A'uB)

I know P(AuB) = P(A) + P(B) - P(AnB)

How can I use that rule to work out the above?

Dreadi · 31 May 2007 at 15:46

These threads make me feel so stupid its unreal

Ricochet J · 31 May 2007 at 15:47

Dry your eyes mate, it's only Stats 1

Rich_L · 31 May 2007 at 15:52

Remind me what the n, u and ' means and I might know....stats was a loooong time ago

NiCkNaMe · 31 May 2007 at 15:56

n - and, u - or? iirc

I swear you make these threads for every question

Ricochet J · 31 May 2007 at 16:01

Nah mate! Must be someone else. Although, I have made a few previous help me threads!

JIM_BOB7813 · 31 May 2007 at 16:02

Ricochet J said:
I need help!

If A and B are two events and P(A)=0.6 and P(B)=0.3 and P(AuB)=0.8 find:

I know P(AuB) = P(A) + P(B) - P(AnB)

How can I use that rule to work out the above?

P(AnB) = P(A) * P(B)

I think

daz · 31 May 2007 at 16:10

The "n" in P(AnB) means the probability of A AND B.

P(AuB) I think means A OR B, which is the same as 1 - P(AnB) (edit, that's only if P(A) and P(B) add up to 1)

The ' is a negation/NOT.

That's all just IIRC.

Have a look at De Morgan's Laws http://en.wikipedia.org/wiki/De_Morgan's_laws for a bit more info on other stuff

Darg · 31 May 2007 at 16:24

I got the first one! yay!

0.8 = 0.6 + 0.3 - P(AnB)

P(AnB) = 0.1

>.>

I don't know what the ' means. Probability of it not happening??

Majago · 31 May 2007 at 16:34

JIM_BOB7813 said:
P(AnB) = P(A) * P(B)

I think

If this holds true then A & B are independent events.

If they're mutually exclusive then P(AnB)=0

delta555 · 31 May 2007 at 16:41

Ricochet J said:
I need help!

If A and B are two events and P(A)=0.6 and P(B)=0.3 and P(AuB)=0.8 find:
a) P(AnB)
b) P(A'nB)
c) P(AnB')
d) P(A'nB')
e) P(AuB')
f) P(A'uB)

I know P(AuB) = P(A) + P(B) - P(AnB)

How can I use that rule to work out the above?

Did these roughly, but i think they are pretty close:
A:0.1
B:0.2
C:0.5
D:0.2
E:0.7
F:0.2

If you draw the diagram with the overlapping circles representing the probabilities of A and B with a bit of overlap between A and B (AnB) then it is relatively easy.

Edit: Yup, just checked them out again and those are the right answers. Just working on a diagram to illustrate it.

Majago · 31 May 2007 at 16:44

Where you say P(A') do you mean the complement (A not occuring)?

Then P(A') =0.4 if P(A)=0.6 and P(B')=0.7.

From this you should be able to do the rest of the questions.

I get :

a) 0.1
b) 0.2
c) 0.5
d) 0.3
e) 0.7
f) 0.2

edit: same as delta - it's easiest to display as a table of probabilites something like:

~ B B' Marginal
A 0.1 0.5 0.6
A' 0.2 0.2 0.4
Marg 0.3 0.7 1

where AnB (0.1) is calculated in part a using your formula. The table is then very easy to fill in and read the results from - sorry it's come up so badly though.

edit2: this link is pretty useful

delta555 · 31 May 2007 at 16:50

Here's a simple diagram:

Just by picking out which bits each part represents then you can easily just add up the different areas.

Darg · 31 May 2007 at 16:59

What happens if you go outside the big circle??