Question

I just need someone to let me know if I am correct here.

The length of an instant message conversation is normally distributed with a mean of 5 minutes and a standard deviation of .7 minutes. What is the probability that a conversation lasts longer than 6 minutes?
0.045
0.077
0.955 ---- this is than answer I chose.
0.922

A study of one thousand teens found that the number of hours they spend on social networking sites each week is normally distributed with a mean of 30 hours. The population standard deviation is 2 hours. What is the 95% confidence interval for the mean?
29.76−30.24 hours
29.88−30 hours
30−30.12 hours
29.88−30.12 hours ---- This is the answer that I chose.

Answer 1

First problem:

Find the z score for raw score 6 minutes:

6 - 5
z = --------- = 1.429
0.7

Using a TI-83 calculator's distribution functions, I found that the area to the right of 6 minutes is

normalcdf(1.428,100) = 0.076