Probabilities & Statistics 1 - OCR (not MEI) - jan 25th 2012 discussion

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also what did u guys get for caclulating the regression line around the middle. i got summit like y= 0.7...x + 78...

i think my answer was fairly wrong though :/

The b value was definitely negative because PMCC was negative, which probably means that your a value is wrong :frown:

Reply 41

Tukazoar

Someone pleaaaaaase post up paper/their answers

Reply 42

MrsNorthman

Did anyone else think the spacing for the questions were reaaaaally weird. Like the one for writing the conditions for geometric distribution was really small, and then the calculating distribution ones were really big??

Reply 43

MrsNorthman

Original post by HypErTwisT

also what did u guys get for caclulating the regression line around the middle. i got summit like y= 0.7...x + 78...

i think my answer was fairly wrong though :/

I got something like that, and that r=-0.9...

Reply 44

Playingwell

Original post by MrsNorthman

Yeah the binomial conditions question was like 4 marks and had like 4 lines :/

Reply 45

c_subs

Original post by MoneyOverEverythin

bi: picking 3 or more odds: 5/14 i think but i remember being pretty certain on whatever answer i did get.

bii: adds up to 28.. 2 ways so 1/63

Can u explain both of these - ie formula +steps

Reply 46

Tukazoar

Original post by c_subs

Can u explain both of these - ie formula +steps

bii. There's only 2 ways to make 28 from 4 of the numbers.

X (9 + 8 + 7 + 4) and
Y (9 + 8 + 6 + 5)

the probability of choosing the X combination is (1/9 x 1/8 x 1/7 x 1/6) which = 1/3024. But there are 4! ways of doing this, as you can pick each number in any order, so its 4! x (1/3024) = 24/3024.

likewise, the probability of choosing the Y combination is exactly the same = 24/3024.

therefore total probability = these two added = 48/3024 which simplifies to 1/63.

Reply 47

HypErTwisT

Original post by Playingwell

The b value was definitely negative because PMCC was negative, which probably means that your a value is wrong :frown:

agh, my mistake, i got a negative. I think i got -0.7 ish

Reply 48

Playingwell

Original post by HypErTwisT

agh, my mistake, i got a negative. I think i got -0.7 ish

That sounds right to me then :biggrin:

Reply 49

c_subs

Original post by Tukazoar

adn what formula did u use for X/Y combination? meaning- how did u get 1/9 x 1/8 x....etc..what's the formula?

Reply 50

c_subs

Original post by MoneyOverEverythin

bi: picking 3 or more odds: 5/14 i think but i remember being pretty certain on whatever answer i did get.

nd how did u get this again? formula?

Reply 51

MoneyOverEverythin

give me a minute for bi..

bii: there were 2 ways of getting 28 with 1,2,3...9. These are 9,8,7,4 and 9,8,6,5. So there are 4! ways of getting each of these so 24x2=48 and there are 3024 ways of picking 4 from 9 (worked out in the first bit of question) so 48/3024 is 1/63

Reply 52

Tukazoar

Original post by c_subs

adn what formula did u use for X/Y combination? meaning- how did u get 1/9 x 1/8 x....etc..what's the formula?

If you pick one card you have one less left than before.
i.e. you start with 9, pick one, you're left with 8, and so on...

it's not a formula, it's common sense

Reply 53

ben1994

Original post by c_subs

can you explain why Geo has the graph of V.

Because in Geometric distribution, the first frequency is always the highest and this then decreases. Like, if you keeps multiplying by a decimal the number is going to get smaller and smaller. Thats why its V.

Reply 54

jammy274

For the last part of question 8 you just had to take P(B=R) (your previous answer) off 1. Then divide by 2.
Because the only possibilities are, that they are the same number, more red or more blue, and because p=0.5 the latter two are equally likely.

Question 9 you had to do P(X=3) and P(X=4). P(X=4) was just 5/9 x 4/8 x 3/7 x 2/6 = 120/3024. P(X=3) was 3 odds and 1 even so 5/9 x 4/8 x 3/7 x 4/6 x 4C3 (because the even can be in 4 places) = 960/3024
960+120=1080/ 1080/3024 = 0.357 or 5/14.

However I'm not sure on the graph questions... I put V and Y but I'm not sure about V anymore..?

(edited 12 years ago)

Reply 55

N1994

Was X the independent value ?
for q 2 ?

Reply 56

dellprinter

for the fequency density one where you had to find out height of the bar, what did it mean by each unit is 2 cm? What was one unit? a single square or as in each unit on the x axis (so 10 of the single squares)

This was so badly worded :angry:

(edited 12 years ago)

Reply 57

Tukazoar

Original post by N1994

Was X the independent value ?
for q 2 ?

yea

Reply 58

c_subs

Original post by ben1994

u mean the frequecy decreases, because the probability of getting 'p' is decreasing?

Reply 59

MoneyOverEverythin

For bi:

i just worked out the way of getting 3odds only out of the 4, which was 5/63 x 4 because u can do it 4 ways (4C3). then you work out odds of getting exactly 4 odds so (5/9)x(4/8)x(3/7)x(2/6) then whatever that is add 20/63 and boom.