SOLUTION: Battery Lifetime is normally Distributed for large samples. The mean lifetime is 500 days and the standard deviation is 61. a. Find the z-score for 550 days. Round to the neares

Question 1156452: Battery Lifetime is normally Distributed for large samples. The mean lifetime is 500 days and the standard deviation is 61.
a. Find the z-score for 550 days. Round to the nearest tenth.
b. What percentage of batteries will last longer than 570 days ?
c. 40.13 % of the batteries will last less than how many days ? Round to the nearest day.
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
z=(x-mean)/sd=(550-500)/61=50/61=0.8 to nearest tenth
b. lasting longer than 70 days, that is z>(70/61) or z>1.15. That probability is 0.1251 or 12.51%
0.4013 is a z-score of -0.25 (invnorm)
-0.25=(x-mean)/61
-15.25=x-500
c. the value is x=484.75 or 485 days
The answers to b and c have been here since the beginning, 12.51% and 485 days
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