Edexcel S3 - Wednesday 25th May AM 2016

justalawyer1998

If you're looking for less than 5 in a discrete distribution, then the most it can be in a continuous distribution is 4.5. If it is less than or equal to 5, then the most it can be is 5.5.

Whoops, I read it as '5 or less'

Reply 501

economicss

3

Please could anyone explain how we find the variance for exercise A question 3f https://771a1ec81340d97ae9ed29694f73dd633b1c7c70.googledrive.com/host/0B1ZiqBksUHNYV1BTbDkxWXZCVmc/CH3.pdf I understand how we find the mean, but I can't figure out the variance, thanks :smile:

Reply 502

Zacken

22

Original post by economicss

Please could anyone explain how we find the variance for exercise A question 3f https://771a1ec81340d97ae9ed29694f73dd633b1c7c70.googledrive.com/host/0B1ZiqBksUHNYV1BTbDkxWXZCVmc/CH3.pdf I understand how we find the mean, but I can't figure out the variance, thanks :smile:

You know that

X \sim N(\mu, \sigma^2) \Rightarrow \frac{X - \mu}{\sigma} \sim N(0, 1)

(it's the standard normal!).

Then

\text{var}(X_1 + X_2 + \cdots + X_{10}) = 1 + 1 + 1 + 1 + \cdots + 1 = 10

Reply 503

Armpits

2

Where can I find 2015 past paper??

Reply 504

MaySouth17

1

Original post by Armpits

Where can I find 2015 past paper??

https://drive.google.com/folderview?id=0B1ZiqBksUHNYRUQxVzVtaHVCQzQ&usp=sharing&tid=0B1ZiqBksUHNYOURWNGt0TU9nTnc

Reply 505

economicss

3

Original post by Zacken

You know that

X \sim N(\mu, \sigma^2) \Rightarrow \frac{X - \mu}{\sigma} \sim N(0, 1)

(it's the standard normal!).

Then

\text{var}(X_1 + X_2 + \cdots + X_{10}) = 1 + 1 + 1 + 1 + \cdots + 1 = 10

Oh yeah completely forgot that! Thank you :smile:

Reply 506

paradoxequation

2

Original post by paradoxequation

How do you solve the questions such as the part b one in the attached solution? I get the LHS, but I'm always a bit unclear on the steps from how they go from < 0.01 to < -2.3632. I understand they are using the percentage points but how exactly do you get there? Thanks.

Original post by paradoxequation

Sorry, forgot to attach...

Anyone help please? Still don't understand.

Original post by paradoxequation

Anyone help please? Still don't understand.

So if you use the percentage points table in the formula book it gives us that the z value for the probability of being greater than 0.01 is 2.3263 however in this question we want the probability to be less than 0.01 so we need the negative of the z value so -2.3263, do you understand from there or would you like me to explain the rest? Hope that helps :smile:

Reply 508

260498

2

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1463900653306.jpg76.2KB

Reply 509

paradoxequation

2

Original post by economicss

So if you use the percentage points table in the formula book it gives us that the z value for the probability of being greater than 0.01 is 2.3263 however in this question we want the probability to be less than 0.01 so we need the negative of the z value so -2.3263, do you understand from there or would you like me to explain the rest? Hope that helps :smile: