You are Here: Home >< Maths

# S1 Probability Question. Watch

1. I = 'that line you see when representing the probability of one event happening on the condition that the other has happened'

Given P(RIS) = 0.5, P(RIS') = 0.4 AND P(S) = 0.6, find:

a) P(R) b) P(SIR) c) P(S'IR) d) P(S'IR')

a) P(R) = 0.46

b) P(SIR) = 0.652

c)
P(S'IR) = 0.348

d) P(S'IR') = ? (answer in the book says 4/9)

Any help would be appreciated.

Thank you
2. Does the "I" stand for intersection?

P(S'IR') = Anything outside P(R) and P(S). So 1 - P(RuS) = P(S'IR').
3. (Original post by Mambo No. 5)
I = 'that line you see when representing the probability of one event happening on the condition that the other has happened'

Given P(RIS) = 0.5, P(RIS') = 0.4 AND P(S) = 0.6, find:

a) P(R) b) P(SIR) c) P(S'IR) d) P(S'IR')

a) P(R) = 0.46

b) P(SIR) = 0.652

c)
P(S'IR) = 0.348

d) P(S'IR') = ? (answer in the book says 4/9)

Any help would be appreciated.

Thank you
you could've written it like this:

P(A | B)
4. (Original post by Mambo No. 5)

d) P(S'IR') = ? (answer in the book says 4/9)

Any help would be appreciated.

Thank you
To find P(S'|R'), you need P(S'nR') which is equal to 1-P(SuR), with the obvious meanings to 'n' and 'u'.
5. (Original post by Dream Eater)
Wow, that was a communication breakdown. To OP: you can use the ' | ' key on your keyboard to avoid confusion. About the question, I may be wrong but I think there is one piece of information missing. I don't think it is solvable for P(R) as it is. Have you missed anything out?

In fact you can even prove that not just one answer exists. If R,S are independent events then P(R) = 0.5 works just fine as well.
Yeah I had know idea I = l or /.

Doh :P

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: December 12, 2010
Today on TSR

Find out how.

### Want £10K to start a business?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.