Planetarion Forums

midge5 · 3 Jun 2003, 19:31

Doing a stats past paper and I am stuck so any help would be appreciatd. Question is:

P(A) = 0.6, P(A u B) = 0.9, P(B|A) = 0.4

Evaluate:

a) P(A n B)
b) P(B)
c) P(A'|B)

I have had to teach myself the entire module and have the exam in 2 days but have no idea what the P(A|B) means heh.

Ragnarak · 3 Jun 2003, 19:35

not done stats for a couple of years and it's slightly different notation to what we used but doesn't one of them mean 'and' and the other is 'or'

?

MrL_JaKiri · 3 Jun 2003, 19:36

P(A|B) = P(A given B)

Bloomers III · 3 Jun 2003, 19:51

Quote:

Originally posted by midge5
have the exam in 2 days but have no idea what the P(A|B) means heh.

wow me too!

a) don't know

b) don't know

c) don't know

looks like i'm screwed. oh well i know lines of regression

Androme · 3 Jun 2003, 19:57

I've got a S1 book here but no I am not going to tell you wot the notations and such mean

Bloomers III · 3 Jun 2003, 19:59

Quote:

Originally posted by Androme2
I've got a S1 book here but no I am not going to tell you wot the notations and such mean

yeah i have an OCR S1 book, and it's completely ****e. their explanations confuse me more than help explain it to me. when a teacher tells me it's fine, they need to learn how ot write coherently!

Androme · 3 Jun 2003, 20:04

Quote:

Originally posted by Bloomers III
yeah i have an OCR S1 book, and it's completely ****e. their explanations confuse me more than help explain it to me. when a teacher tells me it's fine, they need to learn how ot write coherently!

we do Edexcel and follow sets of books written by Heinemann or some group like that - neway, the books are really good compared to the other crap on the market

queball · 3 Jun 2003, 20:12

Quote:

Originally posted by midge5
Doing a stats past paper and I am stuck so any help would be appreciatd. Question is:

P(A) = 0.6, P(A u B) = 0.9, P(A|B) = 0.4

Evaluate:

a) P(A n B)
b) P(B)

P(AuB)=P(A)+P(B)-P(AnB)
0.9=0.6+P(B)-P(AnB)
P(AnB)=P(B)-0.3
P(A|B)=P(AnB)/P(B)
0.4=(P(B)-0.3)/P(B)
P(B)*0.4=P(B)-0.3
P(B)*0.6=0.3
P(B)=0.5
P(AnB)=0.2
there might be a quicker way

Quote:

c) P(A'|B)

=1-P(A|B)
=0.6

MrL_JaKiri · 3 Jun 2003, 20:13

Quote:

Originally posted by Androme2
we do Edexcel and follow sets of books written by Heinemann or some group like that - neway, the books are really good compared to the other crap on the market

Heinemann Modular Mathematsics for Edexcel AS and A-level!

Bloomers III · 3 Jun 2003, 20:16

Queball you just made me feel even worse

Chrism · 3 Jun 2003, 20:23

I was going to do Maths for A Level

Having seen what others have had to put up with I'm glad I didn't. Physics was bad enough ffs.

OldKal · 3 Jun 2003, 20:27

hmmm...at one point i knew all that, i passed my A Level in maths..but that was 3 years ago...

the equations look familiar...

MrL_JaKiri · 3 Jun 2003, 20:27

Mathematics is fantastic.

Androme · 3 Jun 2003, 20:42

Quote:

Originally posted by MrL_JaKiri
Mathematics is fantastic.

Jigglypuff is fantastic.

laney · 3 Jun 2003, 20:45

Quote:

Originally posted by Chrism
I was going to do Maths for A Level

Having seen what others have had to put up with I'm glad I didn't. Physics was bad enough ffs.

physics is awful

MrL_JaKiri · 3 Jun 2003, 20:52

Quote:

Originally posted by laney
physics is awful

That's a really bad typo of 'great' you've got there.

OldKal · 3 Jun 2003, 21:00

physics is great..i remember a lot more of my physics stuff, but that's as i did some physics in my 1st year of my degree too

NEWSBOT3 · 3 Jun 2003, 21:29

to be fair, i enjoyed maths + physics at a-level, i just couldnt do either.

Demon Dave · 3 Jun 2003, 21:30

i'm just about to do my maths GCSE paper 1. then i'm doing A level Maths, Physics, Computing and maybe Electronics at college. looking at that maths stuff makes me question my choices

midge5 · 3 Jun 2003, 21:35

Quote:

Originally posted by queball
P(AuB)=P(A)+P(B)-P(AnB)
0.9=0.6+P(B)-P(AnB)
P(AnB)=P(B)-0.3
P(A|B)=P(AnB)/P(B)
0.4=(P(B)-0.3)/P(B)
P(B)*0.4=P(B)-0.3
P(B)*0.6=0.3
P(B)=0.5
P(AnB)=0.2
there might be a quicker way

=1-P(A|B)
=0.6

hmm different to what i had :/

P(A n B) = P(B|A).P(A)
= 0.4 X 0.6
=0.24

then
P(A u B) = P(A) + P(B) - P(A n B)
0.9 = 0.6 + PB - 0.24
PB = 0.54

c) P(A|B) = P(A n B) / P(B)
= 0.24/0.54 = 4/9

Then P(A'|B) = 1 - P(A|B) = 5/9

poshphil · 3 Jun 2003, 21:37

Quote:

Originally posted by NEWSBOT3
to be fair, i enjoyed maths + physics at a-level, i just couldnt do either.

Sounds like me.

Except I decided to do Astrophysics at uni, like a fool.

MrL_JaKiri · 3 Jun 2003, 22:01

Quote:

Originally posted by midge5
hmm different to what i had :/

P(A n B) = P(B|A).P(A)
= 0.4 X 0.6
=0.24

then
P(A u B) = P(A) + P(B) - P(A n B)
0.9 = 0.6 + PB - 0.24
PB = 0.54

c) P(A|B) = P(A n B) / P(B)
= 0.24/0.54 = 4/9

Then P(A'|B) = 1 - P(A|B) = 5/9

You're right.

Chrism · 3 Jun 2003, 22:14

Quote:

Originally posted by NEWSBOT3
to be fair, i enjoyed maths + physics at a-level, i just couldnt do either.

Physics was ok, I was just really crap at it.

inf · 4 Jun 2003, 11:22

Quote:

Originally posted by laney
physics is awful

No, physics is great.

roadrunner_0 · 4 Jun 2003, 11:30

physics rocked at a level, pity i spent two years in th pub really, but there you go :/

Dr Wakka · 4 Jun 2003, 11:39

Quote:

Originally posted by laney
physics is awful

Where would we be without it? Be fun though to skip gravity once in a while.

ELeeming · 4 Jun 2003, 11:44

Quote:

Originally posted by MrL_JaKiri
Mathematics is fantastic.

OldKal · 4 Jun 2003, 19:43

Physics and Maths at A level...so i decided to do politics at uni :-D

JamMak · 4 Jun 2003, 20:09

Maths and Physics are

Spanish is teh ghey tho... But thats all finished as of today!

I have 7 more exams, some people have finished, hoh well.

And MEI Maths

Deepflow · 4 Jun 2003, 20:20

i did physics and maths at A level... and i was FANTASTIC.

but i just didnt care... hence no homework, and only about 33% attendance... along with a surly attitude

oh bum