# Mini prob. question

• Jan 26th 2009, 06:02 AM
Faisal2007
Mini prob. question
Given $u = 12$ $o = 3$ , what is the probability of P(X<9) ?

I have no clue how to do it...
• Jan 26th 2009, 06:05 AM
galactus
Am I to assume that u is ${\mu}$ for the mean and

o is ${\sigma}$ for the standard deviation?.

If so, $z=\frac{x-{\mu}}{\sigma}$

$z=\frac{x-12}{3}$

If x=9, then z=-1.

What is the z score for -1?.
• Jan 26th 2009, 06:08 AM
Faisal2007
Is it 0.15?

Why did you find the z score though ?
• Jan 26th 2009, 10:54 AM
mr fantastic
Quote:

Originally Posted by Faisal2007
Given $u = 12$ $o = 3$ , what is the probability of P(X<9) ?

I have no clue how to do it...

Please post the whole question. Be sure to include the part about what distribution X follows .....
• Jan 27th 2009, 04:29 AM
Faisal2007
Quote:

Originally Posted by mr fantastic
Please post the whole question. Be sure to include the part about what distribution X follows .....

This is all i have ........... Nothing more or less....
• Jan 27th 2009, 11:18 AM
mr fantastic
Quote:

Originally Posted by Faisal2007
This is all i have ........... Nothing more or less....

Surely you're told the distribution! What is the context of the question? Is it a question from a problem set on normal distribution? Binomial distribution ....?

If you can't provide all the necessary background information to the question you're not going to get much help.