HELP PLEASE STATISTICS

#1
A company makes parts for a machine. The lengths of the parts must be within certain limits or they will be rejected. A large number of parts were measured and the mean and standard deviation were calculated as 3.1 m and 0.005 m respectively. Assuming this data is normally distributed and 99.7% of the parts were accepted, what are the limits?
Выберите один ответ:
a. Between 3.075 m and 3.125 m
b. Between 3.090 m and 3.110 m
c. Between 3.085 m and 3.115 m
d. Between 3.080 m and 3.120 m
 

hlsmith

Less is more. Stay pure. Stay poor.
#2
Sounds like you need to +/- blank times the standard deviation to achieve a 99.7% coverage.