Edexcel S2 - 27th June 2016 AM

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Reply 300

Kevin De Bruyne

Original post by iMacJack

Is part a B = 23/6? I have a feeling I have done something wrong

Correct

Reply 301

imran_

Original post by SeanFM

It's to do with the critical region, the % significance and what value of k is most suitable (see from tables, trial and error)

yeah i thought of that but we're not given any value for Lambda so how would I know where to search

Reply 302

Kevin De Bruyne

Original post by imran_

yeah i thought of that but we're not given any value for Lambda so how would I know where to search

The P(X=<9) column is probably the most useful.

Reply 303

HarunH1

[QUOTE="Bloom77;66112739"]

Original post by Bloom77

ImageUploadedByStudent Room1466931385.585473.jpg

This is what I did so far: ImageUploadedByStudent Room1466931423.250029.jpg

But how do you know it's not the first function but it's the second one?

Help please

Posted from TSR Mobile

i think with part 1 you realise that the first equation contains 0.6 of the overall probability and the second contains 0.4.
If you do F(3) you get 0.3. This means that the rest of the area of the CDF is 0.7. If you were to find P(3<X<a) = 0.642 you'd have to go from 3-4 in the CD which is (0.6 (the whole area under the first equation) - 0.3) = 0.3.

From that 0.3 you realise its less than 0.642 so that means you have to get the rest in the second equation. I would've done F(a) = 0.642-0.3
then solved the second equation=0.342

I dont know if its right but that's how i would've approached it. If you get two results then you choose the one above 3 :smile:

I'll give it a go now.

edit: turns out the way i did it was wrong lol rip me. I looked at your method and it's right atm (i think). But I think you'd use the second equation for the reason i put above (it's somewhere in there lol). I did it your way and i got a=4.855?

(edited 7 years ago)

Reply 304

Kevin De Bruyne

Original post by CherryTea

Anybody know how to do 3b? It's from the june 2013 paper, I looked at exam solution but I still don't understand why you start off with p(x>n), how do we know that we should use it this way around?

That's from the context.

Remember that X is the number of games sold. So X>n means that more than n games are sold. And, from the question, you want that P(X>n) < 0.05 (in english, the probability of selling more than n games, (because they only have n) should be less than 0.05).

Reply 305

imran_

Original post by SeanFM

The P(X=<9) column is probably the most useful.

Sorry im confused :frown:

Reply 306

asda2313

Original post by Superbubbles

Need help on 2015 paper q3b anyone know??

the first equation is a quadratic, and the second equation is a linear line. as the second equation has a negative gradient as the coefficent of X is - this means that the highest point on the PDF would be where X=2 as this is the first point on the linear equation. 6 would be the lowest point. hope this makes sense

Reply 307

psychemma

Does anyone have a full list of definitions we should know?

Reply 308

iMacJack

Original post by SeanFM

Correct

K = -936/391 ?

Again I don't think I'm right xD

Reply 309

Kevin De Bruyne

Original post by imran_

Sorry im confused :frown:

There isn't much else to say :redface:

it is a very difficult question (the replacement paper, I presume) but you've got all the information there and you just need to scan through the different values of lambda and look for the most appropriate one.

Reply 310

Kevin De Bruyne

Original post by iMacJack

K = -936/391 ?

Again I don't think I'm right xD

Afraid not - k is a whole number - actually, let me double check that. I think I've messed it up :lol:

Yes - k should be a whole number. Phew.

(edited 7 years ago)

Reply 311

iMacJack

Original post by SeanFM

Afraid not - k is a whole number - actually, let me double check that. I think I've messed it up :lol:

Yes - k should be a whole number. Phew.

Only other value I get (when I do my calcs properly) is k = 18/23

Maybe I'm doing it wrong though?

I'm integrating between the limits and then just setting = 1?

Reply 312

r3h4f

Original post by SeanFM

The P(X=<9) column is probably the most useful.

I would have thought that it would be P(X<=8) because CR is X>=9?

Reply 313

Kevin De Bruyne

Original post by iMacJack

Only other value I get (when I do my calcs properly) is k = 18/23

Maybe I'm doing it wrong though?

I'm integrating between the limits and then just setting = 1?

integrating what between which limits, and why? (you do have to set something equal to 1, so you are heading in the right direction)

Reply 314

Kevin De Bruyne

Original post by r3h4f

I would have thought that it would be P(X<=8) because CR is X>=9?

imran_

Yes, that is correct - sorry. i didn't put a huge amount of thought into it.

Reply 315

iMacJack

Original post by SeanFM

integrating what between which limits, and why? (you do have to set something equal to 1, so you are heading in the right direction)

F(B) = 1

And integrating both parts of f(x) between their limits and setting = to 1 (because total prob = 1) so then I can find the value of K?

Reply 316

username1626859

Posted from TSR Mobile

Could someone quickly explain to me how to solve 4c Jan 2013?

1466947682390.jpg74.6KB

Reply 317

Kevin De Bruyne

Original post by iMacJack

F(B) = 1

And integrating both parts of f(x) between their limits and setting = to 1 (because total prob = 1) so then I can find the value of K?

Correct (though if you sketch the half of the distribution that you do know, it may help to..save some integrating, is all I will say).

Perhaps something is going wrong in the calculation or writing things down?

Reply 318

iMacJack

Original post by kosvengali

Posted from TSR Mobile

Could someone quickly explain to me how to solve 4c Jan 2013?

Add five to both sides of the inequality and work it out? Take care of the 8 in the inequality though, as the maximum value is 6, so adjust the inequality taking note of this