slack

In 2008, John Cook shared a powerful example of queuing theory: 

If you have one bank teller, an average of 5.8 customers per hour, and an average of 10 minutes required to serve each customer, customers will have to wait almost five hours — an entire afternoon — before being served. 

What happens if you add two tellers? Cook explains, ‘… with a second teller, it’s not likely that even two people will arrive before one of the tellers is free.’ As a result, the average wait time goes all the way down to 3 minutes. 

This is the power of having slack in a system.