Question

The life expectancy (in hours) of a fluorescent tube is normally distributed with a mean 8000 and a standard deviation 1000. find the probability that a tube lasts for more than 11000 hours.

Answer 1

Given that the ,mean is 8000 and the standard deviation is 1000, thus the probability that  tube lasts for more than 11000 hours. will be given by:
P(x>11000)
the z-score is:
z=(x-μ)/σ
x=11000
μ=8000
σ=1000
hence:
z=(11000-8000)/1000
z=3
thus
P(x>11000)=1-P(x<11000)
But
P(x<11000)=P(z<3)=0.9987
hence
P(x>11000)=1-0.9987=0.0013

Answer 2

Answer:

P(x>11000)=1-0.9987=0.0013

Step-by-step explanation: