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 1900.
The Townville Parks Department has just installed 1900 new lightbulbs with an expected mean lifespan of 75 months and a lifespan standard deviation of 12 months. Assuming normally distributed bulb failure, how many bulbs will need to be replaced after 53 months? Round your answer to the nearest whole number.
1 answer