The problem:

"The average annual age of doctors in a certain hospital is 43.0 years old with a standard deviation of 3.0 years. Assume that the variable is normally distributed.

(a) Find the probability that the age of a randomly selected doctor is less than 42.32 years.

(b) Find the probability that the mean age of a sample of 25 randomly selected doctors is less than 42.32 years."

I know that "normal distribution" entails that mean=median=mode which I'm thinking might help me solve for N but I'm still stumped. Thank you!