TKK Products Manufactures Electric Light Bulbs in the 50-, 60-

TKK Products manufactures electric light bulbs in the 50-, 60-, 75-, and 100-watt range. Laboratory tests show that the lives of these light bulbs are normally distributed with a mean of 760 hr and a standard deviation of 60 hr.
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Round your answers to four decimal places, if necessary.
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What is the probability that a TKK light bulb selected at random will burn for more than 820 hr?
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What is the probability that a TKK light bulb selected at random will burn for less than 640 hr?
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What is the probability that a TKK light bulb selected at random will burn between 760 and 820 hr?
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What is the probability that a TKK light bulb selected at random will burn between 640 and 800 hr?
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