4. The manager of an auditorium where pop concerts are often held has found that the attendance to this kind of concert is normally distributed with an average of 6,000 people, and standard deviation 1,500. The tickets are sold at a flat rate of $500 each. Overall, all concert organizers who rent this auditorium lose money on 20% of time. For the upcoming concert, how many people the concert must draw in order for the concert organizer to break even? (17%)

   到場觀眾的數量X 呈 平均數=6000，標準差=1500 的常態分配                    解說：李柏堅

題目告訴我們每辦一次音樂會會有20%虧錢的機率(觀眾太少造成)

                   標準常態分配表

    到場觀眾的數量要4740人才能損益兩平，觀眾4740人以上才能賺錢