The life expectancy of light bulbs whose lifetimes are normally distributed with

Question

The life expectancy of light bulbs whose lifetimes are normally distributed with a mean life of 750 hours and with a standard deviation of 80 hours. a.) What percent of light bulbs will last longer than 870 hours? b.) What percent of light bulbs will last between 730 hours and 850 hours? c.) What percent of light bulbs will last less than 770 hours? d) If the quality control program of the company can consistently eliminate the worst 10% of the bulbs manufactured, the manufacturer can safely offer customers a money-back guarantee on all lights that fail before __________ hours of burning time.

Explanation / Answer

in this case we have U= 750 and s=80 A) here we have 750- 870 from the formula z=x-u/s putting the values Z= 870-750/80 = 1.5 it shows A= 34.98%

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