Question

It feels like I'm going 3 steps forward, but forced to take 5 steps back. :(
I did everything I thought was right but kept getting the answer wrong, need help.

Question:
Normally distributed
Mew=73
STD= 2
If a random sample of thirty 18 year old men is selected, what is the probability that the mean height X bar is between 72 and 74 inches?

Answer 1

what did you do ?

Answer 2

i used the x bar-mew/sigma xbar

so, 72-73/5.4772 and 74-73/5.4772

Answer 3

isn't sigma 2/sqr(18) ?

Answer 4

what do you mean?

i did the standard of error. so, sigma/sq root n

Answer 5

the mean of a sample is the same as the mean of the population
in this case 73

the std dev of the sample is the population std dev divided by the sqr(n)
where n is the sample size.

in this case, population std dev is 2
n is 18
2/sqr(18) = 0.4714

Answer 6

won't it be 30 because the question sample 30 men

Answer 7

oh, yes 30
2/sqr(30) is the standard deviation of the sample mean

Answer 8

so, it would be 5.4772

Answer 9

it would be 2/5.4772 = 0.36515

Answer 10

oooooooooh... dang it lol i just caught my mistake.

Answer 11

so, i just put 0.3652 into my original work?

Answer 12

yes

Answer 13

so, 72 - 73/ 0.3652, 74-73/0.3652

making it -2.74 and 2.74

z score .0031 and .9969

Answer 14

yes, so the probability of falling within that interval is about 99.4%

Answer 15

ok, i got it right and i know what i did wrong. Thanks a bunch!!!! :D

Answer 16

yw