In: Statistics and Probability
The lifetimes of a certain electronic component are known to be normally distributed with a mean of 1,400 hours and a standard deviation of 600 hours. For a random sample of 25 components the probability is 0.6915 that the sample mean lifetime is less than how many hours?
A)1345
B)1460
C)1804
D)1790
Given that,
mean =
= 1400
standard deviation =
= 600
n = 25
= 14000
=
/
n = 600 /
25=120
Using standard normal table,
P(Z < z) = 0.6915
= P(Z < z) = 0.6915
= P(Z < 0.5) = 0.6915
z = 0.5 Using standard normal table,
Using z-score formula
= z *
+
= 0.5 *120+1400
= 1460