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**sinni8** Question 3 .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.

Mr F says: You can't do part (a) ...?

(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.