Question

he physical plant at the main campus of a large state university receives daily requests to replace florescent light-bulbs. The distribution of the number of daily requests is Normally distributed with a mean of 47 and a standard deviation of 10. Using the Empirical Rule, what is the approximate percentage of light-bulb replacement requests numbering between 47 and 57?

Answer 1

Answer:

47.75 %

Step-by-step explanation:

It is a very well known issue that in Standard Normal Distribution  porcentages of all values fall according to:

μ  +   σ       will contain a 68.3 %

μ   +  2σ    will contain  a  95.5 %

μ  +  3σ      will contain  a  99.7 %

However it is extremely  importan to understand that the quantities above mentioned are distributed simmetrically at both sides of the mean, that is,  the intervals are:

[  μ - 0,5σ ;  μ  + 0,5σ ]

[  μ -   1σ ;  μ  +      1σ ]

[  μ -   1.5σ ;  μ  +   1.5σ ]

So we have to take that fact into account when applying the empirical rule. Then

With   mean    μ  =  47       and  σ = 10   is equal to say

values between    47    and     57    (  μ  +   σ  )  we are talking about the second interval, but just half of it.

Then the  approximate porcentage of light-bulb replacement requests is

95.5 /2   =  47.75 %