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

Scroll to see replies

I got the same for all of these. (48/3024 simplifies down to 1/63 - an easier way to do this was just 2/9C4.)

Calculating the Spearman's rank was 1/2. And I think the height of the bar on the histogram was 2/3cm?

for the histograms bit i got 2 for FD and then 1/3 not 2/3

it was something like 2/6 so simplifies down to 1/3

For the one about flowers, was it just (8C7x0.5to8) + (8C8x0.5tothe8) ?

Did u really get 0.412 as well for the being more red flowers? how did you do that one?

Reply 21

MoneyOverEverythin

Original post by Ree69

Yup, well 0.416 I think.

P(more red flowers than blue) =

\frac{P(X\neq 11)}{2} = \frac{1}{2} (1 - P(X=11)) = \frac{1}{2} (1 -(^{22}\mathrm{C}_{11} \times 0.5^{22})) = 0.416

Although I'm not sure if I can remember a 5/14. Something out of 14 does seem familiar. I may have written the decimal equivalent :s-smilie:

.

Oh yeah. 0.357 is familiar. I got it as the answer to the first part of the last question.

Beautiful! for the flowers i even did all 11 ways or so just to check and added them up, it was right!

the one for being more than 3 odds was 5/14 i think, but dont hold me to that. it was definately one of questions 8 or 9.

Reply 22

Ree69

Original post by MoneyOverEverythin

Yeah, that was it - I got 0.357 for the question where they asked the probability of at least 3 of the balls being odd. I think the question was 9bi. (Or 9 ii a :s-smilie:

)

Reply 23

MoneyOverEverythin

Original post by Ree69

Yeah, that was it - I got 0.357 for the question where they asked the probability of at least 3 of the balls being odd. 9bi) I think the question was. (Or 9 ii a :s-smilie:

)

yeah there was 4 parts to 9.

ai: how many ways 9P4 or 9x8x7x6 = 3024
aii: how many of these are odd ... 1680

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

Reply 24

Renn

Original post by Jedicake

I also got 2/3cm too.

For the question where you had the 9 numbered discs, what did people get?
I got 4! for the first part because it said in the question Andrea picks 4 discs and puts them down in a random order. So I thought it was how many arrangements can you be made from the 4 that Andrea picked and not how many different combinations of 4 she could pick...

However, everyone else I've talked to did something like 9C4 instead so I'm thinking I'm probably wrong and got confused reading the question.. :confused:

Reply 25

Ree69

Original post by MoneyOverEverythin

Oh damn, I think I got ai and aii wrong. 5 marks dropped. I wrote the answer as 4! (twice... I should've looked again - I knew something was iffy with that).

Ah well.

Reply 26

tooambitious

How did everyone find it? I somehow got 3 ways for the last question (idiot) and for the binomial graph one I forgot toy writ down the second reason for which binomial graph (again idiot), I'm hoping between 68-70/72 and praying that (like last June) 100ums is around 68, gosh I'd be so happy :biggrin:

Reply 27

spiders-design

Anyone else notice the mistake. For the question where you had to say which graph was the geometric distribution there was a value for 0 which is not possible. Although it wouldn't have prevented anyone from getting that question right they may have then got the next one wrong as they may have thought that it returns the number of failures rather than the number of trials upto and including the success.

I think I got 100 UMS just not sure whether it was 100% or not. Might have made a silly mistake somewhere.

Reply 28

MoneyOverEverythin

Was it 2/3?? or 1/3 wasnt the width of class boundary 6 so 2/6 = 1/3?

Reply 29

c_subs

Original post by ben1994

For the question where you had to match the Geo and Bio distributions to the graphs did anyone get V and Y respectively?

can you explain why Geo has the graph of V.

Reply 30

Jedicake

Original post by MoneyOverEverythin

Was it 2/3?? or 1/3 wasnt the width of class boundary 6 so 2/6 = 1/3?

You forgot the scale of the graph (2cm/unit).

Reply 31

Tukazoar

For the flowers one I just used the calculator,

Binomial C.D

where x = 10
Numtrial = 22
P = 0.5

and got 0.4159 or 4.16. Is that like, cheating? :confused:

Also was the geo graph, V, the one that went down each time ?

(edited 12 years ago)

Reply 32

c_subs

Original post by MoneyOverEverythin

Was it 2/3?? or 1/3 wasnt the width of class boundary 6 so 2/6 = 1/3?

each square/unit = 2cm
and the fequency desity= 1/3
so for the heigh = fequ.density x units/squares = 1/3 x 2 = 2/3 cm

Reply 33

c_subs

Original post by Tukazoar

For the flowers one I just used the calculator,

Binomial C.D

where x = 10
Numtrial = 22
P = 0.5

and got 0.4159 or 4.16. Is that like, cheating? :confused:

where did it say in the qu. that n = 10? nd wat do u mean by C.D

Reply 34

HypErTwisT

i completely failed the very last question...i had no idea, i expected there to be loads of ways to make 28, turns out there was only 2

Reply 35

MoneyOverEverythin

Original post by Jedicake

You forgot the scale of the graph (2cm/unit).

ahh ofcourse! it said it wanted it in cm so i just ended up putting 1/3, damn.

Reply 36

Tukazoar

Original post by c_subs

where did it say in the qu. that n = 10? nd wat do u mean by C.D

x = 10, is the same as x is = or < than 10 on the calculator, which is the same as x < 11, which is what the question asked.

Reply 37

c_subs

Original post by MoneyOverEverythin

what formula did you use...i can't remember

Reply 38

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 :/

Reply 39

Jedicake

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 y = -0.78x + 70 ... My memory is poor.