According to ACT, results from the 2008 ACT test-ing found that students had a mean reading score of 21.4 with a standard deviation of 6.0. Assuming that the scores are normally distributed,
a. find the probability that a randomly selected student had a reading ACT score less than 20.
b. find the probability that a randomly selected student had a reading ACT score between 18 and 24.
c. find the probability that a randomly selected student had a reading ACT score greater than 30.
d. find the value of the 75th percentile for ACT scores.