This discussion is now closed.

Check out other Related discussions

Probability Question: What is the value of P(A u B')?

I am stuck on the following question and would be really grateful if someone could help me out:

1) Events A and B are such that: P(A) = 0.4; P(B) = 0.5; P(A n B) = 0.3; and P(A u B) = 0.6.

i) What is the value of P(A u B')? (Where B' is the compliment of B.)

Reply 1

Swayum

Sorry but I'm not sure what you mean by "compliment". Presuming you mean P(B') = 1 - P(B):

P(AuB') = P(AnB')/P(B')

P(B') = 1 - P(B) = 0.5

P(AnB') = P(A) - P(AnB) (this is visible from a Venn diagram) = 0.1

P(AuB') = P(AnB')/P(B')
= 0.1/0.5 = 0.2.

Could be wrong, I'm not very good at probability.

*Edit*

Ignore the nonsense here.

Reply 2

datr

Here's the venn diagram. The shaded region represents the probability P(AuB'). Can you see what the answer is now?

DeathAwaitsU you have found P(A|B').

venn.gif8.6KB

Reply 3

generalebriety

DeathAwaitsU

Sorry but I'm not sure what you mean by "compliment". Presuming you mean P(B') = 1 - P(B)

That's what complement means, yes. :wink:

Compliment means B' is saying nice things to B.

Reply 4

Swayum

Oh right yeah of course, what was I thinking?

I meant:

P(AuB') = P(A) + P(B') - P(AnB')
= 0.4 + 0.5 - 0.1 = 0.8.

Reply 5

PeterParadox

DeathAwaitsU

Oh right yeah of course, what was I thinking?

I meant:

P(AuB') = P(A) + P(B') - P(AnB')
= 0.4 + 0.5 - 0.1 = 0.8.

How did you get 0.1 for P(AnB')?

Reply 6

generalebriety

PeterParadox

How did you get 0.1 for P(AnB')?

Datr explained it for you with a diagram.

Reply 7

nota bene

P(A)-P(A n B)=P(A n B')

Reply 8

steve2005

nota bene

P(A)-P(A n B)=P(A n B')

I don't think this is correct. I might be wrong, but it looks odd?

Reply 9

Gaz031

generalebriety

That's what complement means, yes. :wink:

Compliment means B' is saying nice things to B.

That made me laugh out loud :smile:

. Presumably anyone in my house who isn't fast asleep now thinks I'm crazy.

Reply 10

onkiratu

between 0.8 and 0.2, which is correct for P(AuB')

Reply 11

crax

P(AuB)=P(A) P(B)-P(A intersection B)
P(AuB')=P(A) P(B')-P(A intersection B')
P(B')=1-P(B) = 1-0.5= 0.5
P(A intersection B') = P(A).P(B') = 0.4*0.5 = 0.2
NOW:
P(AuB') = 0.4 0.5 - 0.2 = 0.7

(edited 6 years ago)

Related discussions

Latest

Trending

Articles for you

Mathematics degree personal statement example (2a) Oxford application

How The Student Room is moderated

To keep The Student Room safe for everyone, we moderate posts that are added to the site.

Try out the app

Continue on web