Z = (score-mean)/SEm
SEm = SD/√n
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score. Multiply by 1100.
The Citiburg Parks Department has just installed 1100 new lightbulbs with an expected mean lifespan of 64 months and a lifespan standard deviation of 8 months. Assuming normally distributed bulb failure, how many bulbs will need to be replaced after 49 months? Round your answer to the nearest whole number.
Please help, I'm having trouble solving this using the excel format they've given and I just can't get it.
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