i have a question in my hw about normal distribution.. and its askin what is the probability that "whatever" exceeds 2.4.

so am i coverting x to Z values to Z to X vaules??

would it be P(x > 2.4) or P(z > 2.4)

wat am i lookin for

Z just tells you how many standard deviations away from the mean it is. if the problem uses their variable (eg mean 2 and standard deviation 1.1), then convert it to z value. if it's asking for "whatever" to exceed 2.4 standard deviations, then it's already in z.

well they give me mean is 2.6 and STD is .5

and they ask what is the probaiblity that whatever exceed 2.4...

so i did

P(x > 2.4)
= P (z > 2.4 - 2.6 / .5) = P (z > -.4) which is equal to 1 - P(z < = -.4)


so...

1 - .34458 = .65542 <-- thats the probability/answer

is this right?

since we know P(z>0) = .5, your answer is going to be a bit more than .5. so that sounds about right.

and instead of saying "whatever", use the random variable X

This post was edited by carteblanche on Oct 19 2013 04:22pm

there was this question askin for the value of sstorm drainage exceeding 95% probability..

I did P (z < x ) =. 95

x - 2.6 / .5 = 1.65

x = 3.425


not sure if my greater or less than sign is correct

obviously, if you switched your sign your answer would be much different. so think about it for a moment. does your answer make sense?

i think so, does it?

X is the value under the normal distribution graph right? the 3.425 is on the far right end of the graph