Let x = age of employee . Assume x is normally distributed with a men of 38 and a standard of 9

what fraction of employees are under the age of 40

if one employee is picked at random, what is the probability that he will be under the age of 40.

If a simple random sample of 100 employee is picked, what is the probability that the sample mean will be less than 40

2. Originally Posted by waterboy
Let x = age of employee . Assume x is normally distributed with a men of 38 and a standard of 9

what fraction of employees are under the age of 40

if one employee is picked at random, what is the probability that he will be under the age of 40.

If a simple random sample of 100 employee is picked, what is the probability that the sample mean will be less than 40
$P(x<40) = P(z<\frac{40-\mu}{\sigma}) = P(z<\frac{40-38}{9}) = P(z<0.222)$

From here find a normal cdf table & you'll be in the money!

3. is this correct

39-38/9 =0.111 = 0.438

40-38/9 = 0.22=0.871

4. Originally Posted by waterboy
is this correct

39-38/9 =0.111 = 0.438
This is all sorts of wrong, firstly

$39-38/9 = 34.78 \neq 0.111$

and

$0.111 \neq 0.438$

I think you mean to say

$\frac{(39-38)}{9} = 0.111$

then

$P(z < 0.111) = 0.54$

from Normal dist table. you really have to be careful with your order of operations!