Probability questions

1. Sep 15, 2008

sinni8

probability questions plz help!!

An engineer wishes to estimate the mean setting time of
a new cement mix used in highway spot repairs. From a record of setting times
for 10 spot repairs he obtain
x = 25; 25; 24; 23; 25; 26; 23; 24; 22; 23
minutes, respectively.
(a) Find the mean and standard deviation of the setting time.

(b) Find a 95% confidence interval for the mean setting time if the standard deviation
is known to be ¾ = 1:5 min: Assume a normal distribution
(c) Find a 95% confidence interval for for the mean setting time if the standard
deviation is unknown.

2. Sep 15, 2008

tiny-tim

Welcome to PF!

Hi sinni8! Welcome to PF!

Show us what you've tried, and where you're stuck, and then we'll know how to help.