# stand norm rand var

• Jan 10th 2009, 07:00 AM
math8553
stand norm rand var
if X~N(-10,25) Find x such that P(X<x)=1/10
i could not find any Ix on the statistical table with value 0.1 so i am stuck,what intermiediate step should i take?
• Jan 10th 2009, 10:56 AM
Constatine11
Quote:

Originally Posted by math8553
if X~N(-10,25) Find x such that P(X<x)=1/10
i could not find any Ix on the statistical table with value 0.1 so i am stuck,what intermiediate step should i take?

If instead it asked for x such that P(X<x)=9/10 would that help.

.
• Jan 13th 2009, 12:11 PM
1234567
Quote:

Originally Posted by Constatine11
If instead it asked for x such that P(X<x)=9/10 would that help.

.

Not really sure what the answer is to this question. Can someone please confirm this. I got two different answer but not sure which one is correct.

1) z = -1.282 (from normal table)

x = z(sigma) + mu = -1.282(5) + -10 = -16.41

2)z = 1.282 (from normal table)

x = z(sigma) + mu = 1.282(5) + -10 = -3.59

Please cans some1 tell me which 1 is correct thanks
• Jan 13th 2009, 12:56 PM
mr fantastic
Quote:

Originally Posted by 1234567
Not really sure what the answer is to this question. Can someone please confirm this. I got two different answer but not sure which one is correct.

1) z = -1.282 (from normal table)

x = z(sigma) + mu = -1.282(5) + -10 = -16.41

2)z = 1.282 (from normal table)

x = z(sigma) + mu = 1.282(5) + -10 = -3.59

Please cans some1 tell me which 1 is correct thanks

X = -16.41 is the answer to the question you originally asked. X = -3.59 was a means of getting that answer.
• Jan 13th 2009, 12:58 PM
1234567
Quote:

Originally Posted by mr fantastic
X = -16.41 is the answer to the question you originally asked. X = -3.59 was a means of getting that answer.

so does this mean for x must be = -16.41
• Jan 13th 2009, 12:59 PM
mr fantastic
Quote:

Originally Posted by 1234567
so does this mean for x must be = -16.41

Quote:

Originally Posted by mr fantastic
X = -16.41 is the answer to the question you originally asked. [snip]

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• Jan 13th 2009, 01:01 PM
1234567
Quote:

Originally Posted by mr fantastic
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Thank you for clearing it up for me, i wasn't to sure about it.