0.81 inch is exactly one standard deviation (s.d.) above the mean of 0.80.
Assuming a normal distribution, you can look up tables, such as:
http://www.math.unb.ca/~knight/utility/NormTble.htm
to find that the probability of not exceeding 1 s.d. above the mean is 0.8413.
Therefore the probability of exceeding 1 s.d. is 1-0.8413.
The diameter of an electric cable is normally distributed, with a mean of 0.8 inch and a standard deviation of 0.01 inch. What is the probability that the diameter will exceed 0.81 inch
1 answer