Hi, can some explain to me, by demonstrating step by step the following questions?

1)Composite scores on the ACT test for the 2013 high school graduating class had mean 21.9 and standard deviation 5.1. In all, 1,899,243 students in this class took the test. Of these, 179,777 had scores higher than 28, and another 56,351 had scores exactly 28. ACT scores are always whole numbers. The Normal N(21.9, 5.1) distribution can include any value, not just whole numbers. What is more, there is no area exactly at 28 under the smooth Normal curve. So ACT scores can be only approximately Normal. (Round your answers to two decimal places.)

• Find the percent of real 2013 ACT scores greater than 28, using the actual counts reported. (Round to two decimal places. Do not include percent sign.)
• Find the percent of 2013 ACT scores greater than or equal to 28, using the actual counts reported. (Round to two decimal places. Do not include percent sign.)
• Find the percent of observations from the N(21.9, 5.1) distribution that are greater than 28. (The percent greater than OR EQUAL TO 28 is the same, because there is no area exactly at 28 for a continuous distribution.)

2) Many companies "grade on a bell curve" to compare the performance of their managers and professional workers. This forces the use of some low performance ratings, so that not all workers are listed as "above average." Ford Motor Company's "performance management process" for a time assigned 10% A grades, 80% B grades, and 10% C grades to the company's 18,000 managers. Suppose that Ford's performance scores really are Normally distributed. This year, managers with scores less than 110 received C grades and those with scores above 459 received A grades. What are the mean and standard deviation of the scores? (Round to one decimal place. This may take multiple steps. You will need to use the z-score formula).

• mean =
• standard deviation =

3) Speeds of automobiles on a certain stretch of freeway at 11:00PM are normally distributed with mean 65 mph. 20% of the cars are traveling at speeds between 55 and 65 mph. What percentage of the cars are going faster than 75 mph? (Do not include percentage sign)