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Edexcel S2 Revision Thread

Reply 80

Jinxxeh

6

916-CALL-TURK

You add them up and divide by two ... :confused:

Noo, it's not like that.. It's like.. All the possible samples (organised by mean) are:
(10 10) Mean = 10
(10 20) (20 10) Mean = 15
(20 20) Mean = 20
(10 50) (50 10) Mean = 30
(20 50) (50 20) Mean = 35
(50 50) Mean = 50

And then you have to do something like.. multiply by the probability of getting them? Possibly? :s-smilie:

It's like.. Urrrrm.. Oh okay, who am I kidding, I have no idea! D:

Reply 81

Jinxxeh

6

Okay, ahh, lots of people being helpful :smile:

So is it like.. The probability of the mean being 10 is 0.25x0.25? = 0.0625
And then the probability of it being 15 is also 0.0625? Or do you have to times that by 2 because there are 2 ways to do it?

Reply 82

laurenlodge

19

Jinxxeh

Noo, it's not like that.. It's like.. All the possible samples (organised by mean) are:
(10 10) Mean = 10
(10 20) (20 10) Mean = 15
(20 20) Mean = 20
(10 50) (50 10) Mean = 30
(20 50) (50 20) Mean = 35
(50 50) Mean = 50

And then you have to do something like.. multiply by the probability of getting them? Possibly? :s-smilie:

It's like.. Urrrrm.. Oh okay, who am I kidding, I have no idea! D:

You make a grid so its like:

x ------------------------------ 10--------------------------------------------15--------------------------------------20
P(X=x)----------------- P(getting two tens) ------------------- 2xP(one ten one twenty) ---------------P(getting two twenties)

etc

Reply 83

916-CALL-TURK

Jinxxeh

Can anyone help me with this question?

I can't work out part c, it's frustrating me! :frown:

The image is too big and i cba to resize, so jus click the link

http://img139.imageshack.us/img139/6466/img0024z.jpg

Reply 84

Jinxxeh

6

Ooooh, I think I've done it :P
x_________10_____15_____20_____30___35____50
P(X=x)__0.0625__0.125__0.0625__0.25__0.25__0.25

:woo:

Reply 85

916-CALL-TURK

Jinxxeh

Noo, it's not like that.. It's like.. All the possible samples (organised by mean) are:
(10 10) Mean = 10
(10 20) (20 10) Mean = 15
(20 20) Mean = 20
(10 50) (50 10) Mean = 30
(20 50) (50 20) Mean = 35
(50 50) Mean = 50

And then you have to do something like.. multiply by the probability of getting them? Possibly? :s-smilie:

It's like.. Urrrrm.. Oh okay, who am I kidding, I have no idea! D:

Check the image, brah :biggrin:

And rotate your head 90 degrees clockwise ...

EDIT: JUST REALISED I PUT 20 INSTEAD OF 10 FML

Reply 86

Jinxxeh

6

916-CALL-TURK

The image is too big and i cba to resize, so jus click the link

http://img139.imageshack.us/img139/6466/img0024z.jpg

Haha, I've done it now but thank you very much anyway!
I was being kinda stupid haha :smile:

Now I must go and face the boredom that is revision of hypothesis testing because I've been avoiding it for the last few days :P

Reply 87

916-CALL-TURK

Jinxxeh

Haha, I've done it now but thank you very much anyway!
I was being kinda stupid haha :smile:

Now I must go and face the boredom that is revision of hypothesis testing because I've been avoiding it for the last few days :P

Haha, I've only just learnt it today :biggrin:

That said - I am quite sick at it :yep:

Reply 88

reem02

I hope they dont ask any tricky f***** up Qs.... other than that I'm ready! =D

Reply 89

shahab1490

Define unrestricted random sampling
simple random sampling
population papameter
uuuuuuuuurghhhhhhhhhhhhhhhhhhh :frown:

too many definitions!!!!

Reply 90

reem02

anyone got a list of all the definitions?

Reply 91

rachaelfowlie

Can someone clarify something for me please? It seems to be pretty hit and miss whether or not I get median questions wrong atm...
So I know you need to do F(m)=0.5, but if F(x) has got 2 or more definitions, which one do you use? Can you just try to solve them both separately, and if the answer you get is actually in the range it's defined for then that's the median?
If that makes sense.
:frown:

Reply 92

uer23

15

rachaelfowlie

Can someone clarify something for me please? It seems to be pretty hit and miss whether or not I get median questions wrong atm...
So I know you need to do F(m)=0.5, but if F(x) has got 2 or more definitions, which one do you use? Can you just try to solve them both separately, and if the answer you get is actually in the range it's defined for then that's the median?
If that makes sense.
:frown:

The way I do it is substitute the upper limit for the first function, for F(x). If the value is greater than 0.5 then you use the first one, if the value is less than 0.5 than it must be in the second one.

Reply 93

reem02

rachaelfowlie

Can someone clarify something for me please? It seems to be pretty hit and miss whether or not I get median questions wrong atm...
So I know you need to do F(m)=0.5, but if F(x) has got 2 or more definitions, which one do you use? Can you just try to solve them both separately, and if the answer you get is actually in the range it's defined for then that's the median?
If that makes sense.
:frown:

you have to see in which function the median(0.5) lies

Reply 94

felt_monkey

12

uer23

The way I do it is substitute the upper limit for the first function, for F(x). If the value is greater than 0.5 then you use the first one, if the value is less than 0.5 than it must be in the second one.

What if the first function value IS 0.5?
I can't get an answer to this...

Reply 95

uer23

15

felt_monkey

What if the first function value IS 0.5?
I can't get an answer to this...

Have you come across such an example before ? I haven't.

Well the limits are covered by less than/less than equal to/more than/more than equal to signs, if there's equal then it must lie in that function.

Reply 96

samir12

OP

16

felt_monkey

What if the first function value IS 0.5?
I can't get an answer to this...

What do you mean? Do you mean that the first F(x) = 0.5?

Reply 97

felt_monkey

12

uer23

Have you come across such an example before ? I haven't.

Well the limits are covered by less than/less than equal to/more than/more than equal to signs, if there's equal then it must lie in that function.