a. (3pts) An observation is drawn from a normal distribution with mean 50 and standard deviation 20 . What is the probability that the observation has a value greater than 81? (Round your answer to 4 decimal points) b. (3pts) An observation is drawn from a normal distribution with mean 400 and standard deviation 40. What is the probability that the observation has a value between 380 and 432 ? (Round your answer to 4 decimal points) c. (3pts) Find the 75th percentile of a normal distribution with mean 100 and standard deviation 30 . (Round your answer to 4 decimal points) d. (3pts) Find the 30th percentile of a t-distribution with 10 degrees of freedom. (Round your answer to 4 decimal points).