Edexcel S3 - Wednesday 25th May AM 2016

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If you were asked find the probability that a student Spends less than 1/3 more than a teacher on reading: P(S< 4/3 T) how you'd set it up? Where s is student and t is teacher

Reply 281

coolguy123456

Original post by Rkai01

If you were asked find the probability that a student Spends less than 1/3 more than a teacher on reading: P(S< 4/3 T) how you'd set it up? Where s is student and t is teacher

Hard to understand phrasing of question the way you've put it but if it's P(S<4/3 T) then you write it as P(S-4/3T < 0) and then write A = S-4/3T. Following this you calculate the combined mean (Mean of S - 4/3 mean of T) and variance (variance of S + (16/9 x variance of T)) and solve it.

Reply 282

Rkai01

Original post by coolguy123456

I just meant the initial set up, that is the hardest bit. The wording can be confusing at times that's all.

Reply 283

etmarks

Question 7d, can someone explain, in quite some detail, would be great!

https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202011%20QP%20-%20S3%20Edexcel.pdf

Reply 284

economicss

Original post by etmarks

Hope this helps :smile:

Reply 285

L'Evil Wolf

Please explain when we use the squared of the Variance in the linear combinations of random variables, when we combine distributions or when we do it normally ..

Reply 286

etmarks

Original post by economicss

Hope this helps :smile:

brilliant thanks, just wondering how the distribution of (x̄-μ) was conjured?

Reply 287

economicss

Original post by etmarks

brilliant thanks, just wondering how the distribution of (x̄-μ) was conjured?

So because the distribution of x bar is in general (mu, sigma squared/n) then the value for (x bar-mu) will be (mu-mu) giving the 0 and we are told that the standard deviation is 3 grams so the variance is (9/n) then we substitute this in to the formula :smile:

Reply 288

L'Evil Wolf

Can someone for q5 explain why the variance is not the smae for the second part of the question:

https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202013%20QP%20-%20S3%20Edexcel.pdf

Why is it 106 and not 52!

Anyone have any resources on this, every time I get this wrong. Done chapter 1 and the review qs

Reply 289

economicss

Original post by L'Evil Wolf

Hope this helps, let me know if you need more explanation :smile:

Reply 290

L'Evil Wolf

Original post by economicss

Hope this helps, let me know if you need more explanation :smile:

Thanks I got the same thing as in working out only the wrong variance, can I ask how you know when to square the variance please?! Like you have done 3^2*3^2 whereas I did 3*3^2 :/

Reply 291

economicss

Original post by L'Evil Wolf

Thanks I got the same thing as in working out only the wrong variance, can I ask how you know when to square the variance please?! Like you have done 3^2*3^2 whereas I did 3*3^2 :/

Does this make sense? :smile:

Reply 292

L'Evil Wolf

Original post by economicss

Does this make sense? :smile:

Thank you this is very helpful.

It is not explained in the edexcel book haha.

Reply 293

economicss

Original post by L'Evil Wolf

Thank you this is very helpful.

It is not explained in the edexcel book haha.

No probs

Reply 294

L'Evil Wolf

http://www.madasmaths.com/archive/maths_booklets/statistics/normal_variables.pdf

@Zacken

Has madas made a mistake on question 2, by neglecting to do the modulus?

the answer should be double that I think?

(edited 7 years ago)

Reply 295

username1162972

Original post by L'Evil Wolf

No he hasn't your finding it given it is greater by 15. Not the difference is 15.
Probability that X2 exceeds X1 by atleast 15 so X2-X1>=15

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Reply 296

L'Evil Wolf

Original post by physicsmaths

No he hasn't your finding it given it is greater by 15. Not the difference is 15.
Probability that X2 exceeds X1 by atleast 15 so X2-X1>=15

Posted from TSR Mobile

Explained very well thank you.