According to the American College Test

(ACT), results from the 2004 ACT testing found that students had a mean reading score of 21.3 with a standard deviation of 6.0. Assuming that the scores are normally distributed:

a. Find the probability that a randomly selected student has a reading ACT score less than 20.

b. Find the probability that a randomly selected student has a reading ACT score between 18 and 24.

c. Find the probability that a randomly selected student has a reading ACT score greater than 30.

d. Find the value of the 75th percentile for ACT scores.