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Answer:
602.50 hours
Step-by-step explanation:
Given that a manufacturing plant uses light bulbs whose life spans are normally distributed, with mean and standard deviation equal to 500 and 50 hours,
It was decided to replace the bulbs so that no more than 2% of the bulbs to burn out between replacement periods
i.e. we have to construct 98% confidence interval right tailed to get this.
Z value is 2.05 for this (Upper tailed 0.98 probability)
Hence margin of error
The upper bound for this would be
So to keep below 2% the bulbs to burn out it should be replaced before 602.50 hours.