Rockwell hardness of pins of a certain type is known to have

Rockwell hardness of pins of a certain type is known to have a mean value of 50 and a standard deviation of 1.7. (Round your answers to four decimal places.)

(a) If the distribution is normal, what is the probability that the sample mean hardness for a random sample of 16 pins is at least 51?

(b) What is the (approximate) probability that the sample mean hardness for a random sample of 40 pins is at least 51?