The number of complaints about food in the school cafeteria per month is a random variable

Question

The number of complaints about food in the school cafeteria per month is a random variable having the normal distribution with μ = 8.3 and σ = 1.8, find the probability that in any month there will be more than 10 complaints.

Answer 1

"More than 10" complaints is 11 complaints.

 

z = (Score - Mean) / SD = (11 - 8.3) / 1.8 = 1.5

 

In Excel, enter this into a cell:

 

=normsdist(1.5)

 

and hit enter

 

The result is the area under the curve which falls below z=1.5

The result is 0.9332 .

 

You are looking for the area above z=1.5, so it is 1 minus that value.

1-.9332 = 0.0668