# Rational Function Question

1. Dec 15, 2007

### tachu101

1. The problem statement, all variables and given/known data
Queuing Theory (study of lines for stores) says that for a drive through window at a Macdonalds, the function

f(x)= 9/(x(x-9))

represents the average time in hours a customer will wait in line. X=average number of people an hour.
How long will a customer have to wait in line (on average)?

3. The attempt at a solution

Not sure at all on how to find an average time out of this function.

2. Dec 15, 2007

### Kurdt

Staff Emeritus
Were you given a value for x?

3. Dec 15, 2007

### tachu101

The question I think says 9<x<or=20

4. Dec 15, 2007

### HallsofIvy

Staff Emeritus
Yes, x will have to be larger than 9 for that function to be positive- and I've never had a negative waiting time at McDonald's! The average of a function, f(x), over $a\le x\le b$ is
$$\frac{\int_a^b f(x)dx}{b-a}$$