Operations Management Calculation Formula Help

[Robert_Conklin]

Good morning.

I am working on a problem in my Operations Management class and am having a problem with a calculation formula.

Question:
Wanda's Car Wash & Dry is an automatic, five minute operation with a single bay. On a typical Sunday morning, cars arrive at a mean rate of 8 per hour, with arrivals tending to follow a Poisson distribution. Find the following:
a. The average number of cars in line.
b. The average time cars spend in line and service.

I can do the math manually and get the correct answer. When I create the formula in excel to do the calculation, I cannot figure it out. Below is what I have:
A B C D E F G H I

λ	8	cars per hour
μ	5	1 car per 5 minutes	12	cars per hour
Ls
Lq
r					A.
p					Lq = λ^2 / 2μ(μ - λ)		-2.13333	'=SUM((B77)^2/((2*B78)*(B78-B77)))
Wq
Ws					B.
1/μ					Ws = Lq / λ + 1 / μ		-0.06667	'=SUM((B80/B77)+(1/B78))
P0
Pn
M
Lmax

Any help or direction would be greatly appreciated.

 

[JimM]

Is -2.13333 and -0.06667 the correct answers or is that the result you are getting with the formulas

 

[Robert_Conklin]

B80 is referencing H82. I deleted it before I took the screenshot. Sorry. The formula for question B relies on the answer for Question A be correct.