The board of examiners that administers the real estate broker's examination in a certain state found that the mean score on the test was 591 and the...

The board of examiners that administers the real estate broker’s examination in a certain state found that the meanscore on the test was 591 and the standard deviation was 72. If the board wants to set the passing score so that onlythe best 80% of all applicants pass, what is the passing score? Assume that the scores are normally distributed. (I understand how to set it up, but for some reason im not getting the answer of 530.52, I do .8= (M-591/72) , i look up .8(.2881), and i still get wrong answer, help!! thanks)