It has been found that times taken by people to complete a particular tax form follow a normal distribution with mean 100 minutes and standard deviation 30 minutes. A random sample of nine people who have completed this tax form was taken. What is the probability that the sample mean time taken is more than two hours?

Question

jim_thompson5910 · Answer

how far did you get with this?

b77w · Answer

I started calculating something expected values or something but i cant seem to find a formula for probability and samples

jim_thompson5910 · Answer

first thing to do is rewrite 2 hrs as 120 minutes

jim_thompson5910 · Answer

we're going to be working with the sample mean distribution (basically the distribution of xbar)

so that tells us the 

mean = mu
standard deviation = sigma/sqrt(n)

hopefully this looks familiar?

b77w · Answer

Yeah i have that

jim_thompson5910 · Answer

ok what is the standard deviation of this particular sample mean distribution?

jim_thompson5910 · Answer

$$\Large SE = \frac{\sigma}{\sqrt{n}} = \frac{30}{\sqrt{9}} = ??$$

b77w · Answer

10