The time, in hours, that a copying machine may work without breaking down is a normally distributed random variablewith the mean549 and the standard deviation68. Find the probabilitythat the machine will work for at least 500 hours without breaking down – explain your answer (study guide problem 59).
Total annual textbook sales in a certain discipline are normally distributed. 45% of the time, sales are above 671,000 copies, and 10% of the time the sale are above 712,000 copies. Find the mean and the varianceof annual sales – explain your answer (study guide problem 72).
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