Question 1172465: The mean life of stockings used by an army was 40 days with SD of 8 days. Assume the life of stockings follows normal distribution. If 100000 pairs are issued, how many would need replacement (i) before 24 days (ii) after 56 days?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Before 24 days is a z of -2, where z=(24-40)/8
probability of that is 0.0228
number of pair would be 100000*0.0228=2280. Note, depending upon where one rounds, either table or calculator, the result will be different.
After 56 days is the same number, because that is more than 2 sd above the mean, and the distribution is symmetrical.
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