level of significant. pls tell me if im correct

#1
A training program for the operation of a piece of diagnostic equipment usually takes an average of 40 hours to complete. A new method of training has been devised with the intent of reducing the mean completion time. A random sample of 25 students taught by the new method showed a mean completion time of 38 hours and a standard deviation of 3.33 hours. At a 0.05 level of significance, has the new method of training reduced the mean completion time?

Pls tell me if im correct

Thanks in advance

WORK DONE :

Zcal=30-40 /{3.33/ 25(square root)} =-2/0.666= -3.003

Z=1.645

at a o.05 level of significance the new method of training has reduced the mean completion time by -3.003hrs
 
#2
since you are using the SAMPLE standard deviation you must use a t-test.

also this is a one tailed test so your z-critical is wrong.

jerry