SOLUTION: The effective life of a battery cell is considered to be normally distributed with the mean of 20 hours and a standard deviation of 5 hours. In a consignment of 100 battery cells,

Question 1142500: The effective life of a battery cell is considered to be normally distributed with the mean of 20 hours and a standard deviation of 5 hours. In a consignment of 100 battery cells, how many cells are expected to have life
(i) less than 15 hours (ii) more than 30 hours (iii) between 8 and 16 hours
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
z=(x-mean)/sd
so < (15-20)/5 or <-1 which is probability of 0.1587
would expect 16 to have life fewer than 15 hours
more than 3 hours is >2 sd or probability 0.0228. This would be 2 cells
between 8 and 16 hours is z between -12/5 and -4/5 or between -2.4 and-0.8
This has probability of 0.2037, so would expect 20 batteries
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