Turn on thread page Beta
    Offline

    11
    ReputationRep:
    (Original post by Molly_xox)
    Yeah, +0.5...

    38-50/sq rt(50) = -1.697, and I thought you needed to compare it to -1.645?
    Isnt the test supposed to be (X+0.5)-50/rt(50) ? So you'd 38.5-50/rt(50) ?

    I'm not 100% sure, you may very well be right
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Molly_xox)
    Yeah, +0.5...

    38-50/sq rt(50) = -1.697, and I thought you needed to compare it to -1.645?
    I think the continuity correction had to be -0.5 since we were finding P(X<x)
    Offline

    0
    ReputationRep:
    can someone please write out the 2 simultaneous equations they got for question 1, i think i made a very stupid error
    thanks!
    Offline

    1
    ReputationRep:
    (Original post by tokopoko)
    I felt pretty good about all my answers, ill post as many as i can remember.

    a=6 then a=1.5 for cont dist qn

    Mean = 146, S.D=2 for normal qn

    Very last qn was something like:
    1/3(0.6 + 0.03) <-- i really cant remember
    So P(type 2 error) = 0.23 ish

    So P(X at least 1 out of 4) = 1 - P(X=0) = 1- (1-0.23)^4
    Yep I got exactly the same as you for all the questions.
    7ii I got 37 (critical value was like 38.4 and then continuity correction so its 37.9 and then you round down to 37)
    Offline

    11
    ReputationRep:
    (Original post by lllllllllll)
    I think the continuity correction had to be -0.5 since we were finding P(X<x)
    I thought we were finding P(X less than or equal to x) ?
    Offline

    1
    ReputationRep:
    (Original post by lllllllllll)
    I think the continuity correction had to be -0.5 since we were finding P(X<x)
    ye i thought so too. i.e. P(X<38) would change to P(X<37.5)?
    Offline

    0
    ReputationRep:
    Can someone give the equation for question 6) I think I looked at the equation wrong because I got a = 1/6 and 6
    Offline

    6
    ReputationRep:
    (Original post by Archer61)
    Can someone give the equation for question 6) I think I looked at the equation wrong because I got a = 1/6 and 6
    Think it was something like 1.5a^-3 * x^2
    Offline

    1
    ReputationRep:
    (Original post by Younjaxx)
    Yep I got exactly the same as you for all the questions.
    7ii I got 37 (critical value was like 38.4 and then continuity correction so its 37.9 and then you round down to 37)
    please explain why you got 37.9, i thought C.Correction was done before not after the test
    Offline

    2
    ReputationRep:
    just realised for the first one I did it as sigma^2, when the formula means it'd be sigma, so I got sigma^2 = 2 and thus sigma = sqrt(2)
    would I lose a mark for this? Suppose I would do, looking at a past paper with a similar question doesn't seem to allow sigma^2
    Offline

    1
    ReputationRep:
    (Original post by AMDD)
    What did everyone get as the value for a for each part of the questions? I got a=6 for both....
    part two was 1.5 and I know the mistake you made because I made the same mistake, when calculating E(X) it was 1/(2a^3) * ( (1/4)x^4) between a and -a so if you put that in you get 1/(2a^3) 8 ((1/4)a^4 - 1/4a^4) the mistake you made was to put ((1/4)a^4 + ((1/4)a^4) but remember that -a^4 is a^4 so if you integrate it you get E(X) as 0. hope it makes sense
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by rich1334)
    I thought we were finding P(X less than or equal to x) ?
    (Original post by tokopoko)
    ye i thought so too. i.e. P(X<38) would change to P(X<29.5)?
    Possible...I don't remember Q7 off the top of my head. All I remember is a continuity correction with -0.5
    Offline

    1
    ReputationRep:
    (Original post by tokopoko)
    please explain why you got 37.9, i thought C.Correction was done before not after the test
    Because you're working backwards. So what I did was say ok so what value of x gives us z of 0.05 and that gave me x as 38.4 or something. And then I was like ok if we're saying that x=38.4 is the critical region, we must've had 37.9 which we then corrected to 38.4 so the actual value of x is 37.9 and the answer is 37. So imagine you wanted to work out the P(x=<38) you would actually work out P(x=<38.5) so if you have P(x=<38.4) the original thing you wanted to find out was P(x=<37.9) makes sense?
    Offline

    0
    ReputationRep:
    were the 2 simultaneous equations for question 1:
    150-u=2(sigma)
    and
    u-146=2(sigma)
    thanks
    Offline

    13
    ReputationRep:
    (Original post by rich1334)
    Isnt the test supposed to be (X+0.5)-50/rt(50) ? So you'd 38.5-50/rt(50) ?

    I'm not 100% sure, you may very well be right
    I hadn't even thought about that...but then you can't have half a signal failure?

    (Original post by lllllllllll)
    I think the continuity correction had to be -0.5 since we were finding P(X<x)
    Yeah that might be where I went wrong, I thought it was strange that I was rounding up...
    Offline

    0
    ReputationRep:
    (Original post by Younjaxx)
    part two was 1.5 and I know the mistake you made because I made the same mistake, when calculating E(X) it was 1/(2a^3) * ( (1/4)x^4) between a and -a so if you put that in you get 1/(2a^3) 8 ((1/4)a^4 - 1/4a^4) the mistake you made was to put ((1/4)a^4 + ((1/4)a^4) but remember that -a^4 is a^4 so if you integrate it you get E(X) as 0. hope it makes sense
    Thatnkyou so much for replying and i think i followed that but why would it not be (1/2a^3)*((1/4)a^4- - (1/4)a^4) inside the brackets which is where i seem to have gone wrong
    Offline

    1
    ReputationRep:
    (Original post by Younjaxx)
    Because you're working backwards. So what I did was say ok so what value of x gives us z of 0.05 and that gave me x as 38.4 or something. And then I was like ok if we're saying that x=38.4 is the critical region, we must've had 37.9 which we then corrected to 38.4 so the actual value of x is 37.9 and the answer is 37. So imagine you wanted to work out the P(x=<38) you would actually work out P(x=<38.5) so if you have P(x=<38.4) the original thing you wanted to find out was P(x=<37.9) makes sense?
    hmm, ive never seen that before. you may be right but i would never think to do that. hopefully someone else can confirm
    Offline

    1
    ReputationRep:
    (Original post by thickmaster)
    I stored all my answers in my calculator and here they are (I think 8ii is wrong):
    1. Mean = 146, sigma = 2
    2. i) The rabbits occur independent of each other
    ii) 0.222 (Using poisson)
    3. i) a = 6
    ii) a = 1.5
    4. 0.8311
    5. 0.2536
    6. 0.9807
    7. i) 0.1247
    ii) 38
    8. i) 0.0316
    ii) 0.961 (I did 1 - (1/3((1-0.9685)+(1-0.6047)+(1-0.0933)))^4)
    I think 8ii is wrong as the probability of getting a type II error when p=0.3 was 0 as you would've accepted H0 correctly rather than erroneously so there was no error.


    Posted from TSR Mobile
    Offline

    0
    ReputationRep:
    (Original post by AMDD)
    Thatnkyou so much for replying and i think i followed that but why would it not be (1/2a^3)*((1/4)a^4- - (1/4)a^4) inside the brackets which is where i seem to have gone wrong
    Substituting -a into x^4 gives you -a*-a*-a*-a giving you positive a^4.

    Also anyone remember how many marks question 3 was worth?
    Offline

    1
    ReputationRep:
    (Original post by iwishiwasclever)
    were the 2 simultaneous equations for question 1:
    150-u=2(sigma)
    and
    u-146=2(sigma)
    thanks
    150 - U = 2 sigma
    146 - U = -1.5 sigma pretty sure they didnt both have 2 in
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: June 13, 2015

2,809

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should predicted grades be removed from the uni application process

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

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