BUS 230-The average lifespan of a brand X light bulb is 48

Question
The average lifespan of a brand X light bulb is 48 months and the variance is 100 months.

a) What percent of light bulbs last longer than 60 months?

b) What percent of light bulbs last between 25 and 55 months?

c) What is the highest number of months a light bulb will last that is in the bottom of 20% of the distribution?

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