Question 1106014: A company installs 5000 lightbulbs, each with an average life of 500 hours, and a standard deviation of 100 hours. Find the percentage of bulbs that can be expected to last the period of time specified assuming the data is normally distributed. At least 500 hours.
between 500 and 675 hours
between 540 hours and 780 hours
more than 650 hours
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A company installs 5000 lightbulbs, each with an average life of 500 hours, and a standard deviation of 100 hours. Find the percentage of bulbs that can be expected to last the period of time specified assuming the data is normally distributed. At least 500 hours.
z(500) = (500-500)/100 = 0
P(x >= 500) = P(z >= 0) = 0.5
------------------------------------
between 500 and 675 hours
z(675) = (675-500)/100 = 175/100 = 1.75
P(500< x <675) = P(0< z < 1.75) = normalcdf(0,1.75) = 0.4599
---------------------
between 540 hours and 780 hours
Find the z-value of 540 and of 780
Then p(540< x < 780) = P(z is between the 2 z-values you found)
------------------------------
more than 650 hours
Use the z-value of 650 to find the answer
---------
Cheers,
Stan H.
-----------
|
|
|
