# Edexcel S2 Exam Paper January 2011 14/01/11 Watch

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#41

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The variable T Distributed by N(8, 4), why does P(T = 5) = 0?

Isn't it meant to be P(4.5 < T < 5.5)?

**jit987**)The variable T Distributed by N(8, 4), why does P(T = 5) = 0?

Isn't it meant to be P(4.5 < T < 5.5)?

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#42

**jit987**)

The variable T Distributed by N(8, 4), why does P(T = 5) = 0?

Isn't it meant to be P(4.5 < T < 5.5)?

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#43

(Original post by

Because with a normal distribution, the probability that it occurs at a single point is always zero, you can only use a normal distribution when investigating the probability a value is above, below, between two certain points, i.e. an inequality. When you change the probability, like from P(T=5) to P(4.5 < T < 5.5), you're thinking about when you change the type of distribution, or something like that, it's been a while.

**Noble.**)Because with a normal distribution, the probability that it occurs at a single point is always zero, you can only use a normal distribution when investigating the probability a value is above, below, between two certain points, i.e. an inequality. When you change the probability, like from P(T=5) to P(4.5 < T < 5.5), you're thinking about when you change the type of distribution, or something like that, it's been a while.

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#45

(Original post by

What's wrong in that statement?

**Noble.**)What's wrong in that statement?

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#46

(Original post by

I was being sarcastic - now that I read back I wasn't being clear enough sorry. You actually explained it very well for someone who potentially hasn't done this for a year.

**anshul95**)I was being sarcastic - now that I read back I wasn't being clear enough sorry. You actually explained it very well for someone who potentially hasn't done this for a year.

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#47

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Haha, I was interested to see how much of it was nonsense after not doing it for a while. I have a pretty good memory, so tend not to forget maths, even if it is useless.

**Noble.**)Haha, I was interested to see how much of it was nonsense after not doing it for a while. I have a pretty good memory, so tend not to forget maths, even if it is useless.

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#48

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#49

how do you know when too use the continuity correction? and if so when do you -0.5 and +0.5??

thanks

thanks

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#50

(Original post by

how do you know when too use the continuity correction? and if so when do you -0.5 and +0.5??

thanks

**gupta21**)how do you know when too use the continuity correction? and if so when do you -0.5 and +0.5??

thanks

**normal distribution**.

Example:

when the discrete distribution is

P(X<17)

continuous would be

P(X<16.5)

BUT

when the discrete distribution is

P(X>17)

continuous would be

P(X>17.5)

ALSO: because for a normal distribution you cannot approximate 'equals to' so,

when the discrete distribution is

P(X?17) [The '?' should be 'less than/equal to' everytime I save it changes to '?' sorry about that )

continuous would be

P(X<16.5)

So when you are calculating the probability for X 'LESS THAN', you'd use the lower bound of X

and

when you are calculating the probability for X 'GREATER THAN', you'd use the upper bound of X

Hope that helps

Good luck!

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#54

(Original post by

Hope Sampling Distribution question pops up

**jit987**)Hope Sampling Distribution question pops up

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(Original post by

Hope Sampling Distribution question pops up

**jit987**)Hope Sampling Distribution question pops up

(Original post by

....

**Noble.**)....

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#56

For the continuity correction

when the discrete is P(x>17)

isnt the continuous P(x>16.5) the lower band?

when the discrete is P(x>17)

isnt the continuous P(x>16.5) the lower band?

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#57

(Original post by

For the continuity correction

when the discrete is P(x>17)

isnt the continuous P(x>16.5) the lower band?

**Foxer27**)For the continuity correction

when the discrete is P(x>17)

isnt the continuous P(x>16.5) the lower band?

and the reason being for this is because we want values above 17 and 16.5 can be rounded DOWN to 16 than 17

hope that helps

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#58

**Foxer27**)

For the continuity correction

when the discrete is P(x>17)

isnt the continuous P(x>16.5) the lower band?

If it would have been , then it would be

If I'm wrong please correct me

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#59

(Original post by

If you can handle those from 01-10 and solomon's very well, then there shouldn't be any problem. How did you find the solomon's?

**jit987**)If you can handle those from 01-10 and solomon's very well, then there shouldn't be any problem. How did you find the solomon's?

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#60

(Original post by

solomons were ok...i hope nothing like P(4<X<5) comes because i alwys mess up those....any particular tricks to learn how to solve those??

**Geniusmiss**)solomons were ok...i hope nothing like P(4<X<5) comes because i alwys mess up those....any particular tricks to learn how to solve those??

For a PDF question if the questions says P(x=5) is it always 0 or is that only for CDF?

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