Statistics help please.

Hi all. No... I don't want you to do my homework for me. But please, help teach me how to do this. It's for an intro Statistics class.

Suppose a simple random sample of size n = 36 is obtained from a population with u (mean) = 64 and o (std. dev.) = 18.

a)describe the sampling distribution of X (sample mean).
b)What is P(x < 62.6)?
c)What is P(x > or = to 68.7)?
d)what is P(59.8 < X  < 65.9)?

Please help walk me through this so i can see how it is done.
The X is actually the X with the line over it for the sample mean.

Answer is c

>>2
he's talking out of his arse, it's a trick question, the answer is e) none of the above

Heh, I should have waited until the trolls went to bed before I asked this. Because if you look at it you can see that the
A)
B)
C)
D)

are just different parts of the question, and not answers.

>>4
you must be new here

>>5
Trolling and flames are not allowed outside of /b/. Unfortunately, it's quite the opposite.

OK, (a)the sampling distribution of sample means is the set of all possible sample means when you take every possible sample of given size n from the population.  The mean of sample means is happily the same as the mean of the population itself, always.  So part of your answer is, mean = 64.  The standard deviation of sample means is the standard deviation of the population divided by the square root of the sample size n.  So the other part of your answer is, standard deviation = 18/√(36) = you could figure the rest.

(b) to (d) Standardize the sample mean x-bar x figures to make standard normal distribution z-scores, and use whatever method at your disposal that you use when you figure probabilites from z-scores.  For the distribution of sample means x, the formula for z is a little different than what you first learned, because remember that the standard deviation of the sample means is the standard deviation of the population divided by the square root of the sample size n, not simply population standard deviation itself.  z = (x - 64)/(18/√(36))

>>6
bahahahha hahahahah!!!! not allowed? who's gonna stop me? the troll police?!!!

Did somebody call for The Troll Police?

Also of note is that if your sample size is low (rule of thumb says less than about 30), the population distribution must be fairly normal for the sampling distribution to be normal. Of course, the lower the sample size, the more normal the population must be if you want to use the normal approximation for calculating sampling probabilities.

If you come across a test item that uses a low sample size and doesn't mention the shape of the population distribution, mention that your calculations are based on the assumption that the population is normal.

k. in your graphing calculator, hit 2nd vars (for dist menu). select normcdf. lower limit is the lowest #. if you are asked P(x<10) then your lower limit is infinity ( enter 1ee99 by hitting 1, ee ( which is 2nd then the comma button) then 99) enter your upper limit (10) enter your mu, then enter your o.
if you are asked P(x>10) then your lower limit is 10, your upper limit is infinity, enter your mu, then your o.

if you are asked p(10>x>20) then your lower limit is 10, upper limit is 20, then enter your mu and o.

im doing the exact homework you are doing right now, so i hope this helps.

>>10
>>11
2009-04-08
2011-11-20

i hope this helps.