Edexcel S2 - 27th June 2016 AM

OP

Original post by RetroSpectro

Im confused as to what they have done for question 7C in the mark scheme, I thought you would decrease each boundary in the uniform distribution by 5 then work out the probability of <2

https://ef8b5216a7366459ac0f2ce0ac13ad2bbcf4d40a.googledrive.com/host/0B1ZiqBksUHNYQVk0YTh4MUlET0E/for-Edexcel/Solomon%20C%20QP%20-%20S2%20Edexcel.pdf

MS: https://ef8b5216a7366459ac0f2ce0ac13ad2bbcf4d40a.googledrive.com/host/0B1ZiqBksUHNYQVk0YTh4MUlET0E/for-Edexcel/Solomon%20C%20MS%20-%20S2%20Edexcel.pdf

|x| is the modulus function - it returns x if x is positive, and -x if x is negative.

So

|x-5| < 2 \Rightarrow (x-5 < 2) \cup (5 - x < 2)

.

The first case is where x-5 is positive, so returns x-5. The second case is where x-5 is negative, so returns 5-x.

You then work with those inequalities and solve the question.

(edited 7 years ago)

Reply 565

iipebblesii

1

If you use a graphical calculator to find the answer to the distribution questions and you get the answer right do you get all the marks for the question including method marks, or do you have to use the tables to work everything out?

Reply 566

RetroSpectro

Original post by SeanFM

|x| is the modulous function - it returns x if x is positive, and -x if x is negative.

So

|x-5| < 2 \Rightarrow (x-5 < 2) \cup (5 - x < 2)

.

The first case is where x-5 is positive, so returns x-5. The second case is where x-5 is negative, so returns 5-x.

You then work with those inequalities and solve the question.

Thanks, didn't realise they used modulus in such situations in stats :u:

Reply 567

OP

Original post by JammyW15

When using an approximation, Say you have X~B(100,0.5) and you want to approximate it into a normal distribution... Do you still use the RV of X, or do you change it, or does it not matter?

You change the letter (well, it's good practice to, not sure if it affects marks) when you change the duration or quantity of something in the definition of something, even if the other parameters were the same. Eg if I said X = number of heads from a fair coin in 5 tosses, X~B(5,0.5) but if I then said 10 tosses it would have to be Y = number of heads in 10 tosses, Y~B(10,0.5).

But when you're approximating, you're modelling the same thing, so you can say that X~B(50, 0.2) and by approximation, X~Po(10) as well.

Reply 568

https://57a324a1a586c5508d2813730734691051ac35fd.googledrive.com/host/0B1ZiqBksUHNYZ3M4QzJ0N19IeHc/January%202009%20QP%20-%20S2%20Edexcel.pdf

Q3a.

I really dont understand how to work out the lower critical values.... I seem to get the upper ones right but the lower ones always wrong. I got upto (X<<L) << 0.05 then what value would you look at.

Reply 569

sana_97

How many past papers should have you done before the exam?

Reply 570

Someone please answer...
https://57a324a1a586c5508d2813730734691051ac35fd.googledrive.com/host/0B1ZiqBksUHNYZ3M4QzJ0N19IeHc/January%202012%20QP%20-%20S2%20Edexcel.pdf
Question 6e

Reply 571

https://57a324a1a586c5508d2813730734691051ac35fd.googledrive.com/host/0B1ZiqBksUHNYZ3M4QzJ0N19IeHc/January%202012%20QP%20-%20S2%20Edexcel.pdf

Q5b too please/???

Reply 572

Kitkat5

3

5. Four coins are flipped together and the random variable H represents the number of headsobtained. Assuming that the coins are fair,
Given that the four coins are all biased such that the chance of each one showing a head is50% more than the chance of it showing a tail,
(d) find the probability of obtaining more heads than tails when the four coins are flippedtogether.

how would you guys do this? i'm so confuuzzled

(edited 7 years ago)

Reply 573

OP

Original post by Kitkat5

5. Four coins are flipped together and the random variable H represents the number of headsobtained. Assuming that the coins are fair,
Given that the four coins are all biased such that the chance of each one showing a head is50% more than the chance of it showing a tail,
(d) find the probability of obtaining more heads than tails when the four coins are flippedtogether.

how would you guys do this? i'm so confuuzzled

What, from one coin, is the probability of getting a head?

Reply 574

Kitkat5

3

Original post by SeanFM

What, from one coin, is the probability of getting a head?

Exactly, Idk? I thought it would be 3/4 but the mark scheme says 3/5 :frown:

Reply 575

JammyW15

8

Original post by SeanFM

You change the letter (well, it's good practice to, not sure if it affects marks) when you change the duration or quantity of something in the definition of something, even if the other parameters were the same. Eg if I said X = number of heads from a fair coin in 5 tosses, X~B(5,0.5) but if I then said 10 tosses it would have to be Y = number of heads in 10 tosses, Y~B(10,0.5).

But when you're approximating, you're modelling the same thing, so you can say that X~B(50, 0.2) and by approximation, X~Po(10) as well.

Ah alright. Thanks again!

Reply 576

Yua

14

anyone have a list of definitions?

Reply 577

OP

Original post by Kitkat5

Exactly, Idk? I thought it would be 3/4 but the mark scheme says 3/5 :frown:

How strange.. I can't see how they've got that :redface:

Reply 578

The probability of an electrical component being defective is 0.075 The component is supplied in boxes of 120

(a) Using a suitable approximation, estimate the probability that there are more than3 defective components in a box.(5)

A retailer buys 2 boxes of components.

(b) Estimate the probability that there are at least 4 defective components in each box.(2)

Reply 579