Little's Law is an equation that expresses the relationship between the processing speed, work-in-process inventory and cycle time for a stable process. This relation provides the basis for using lean methods to reduce processing Lead Times, either by reducing the items in inventory, or by increasing the throughput rate or processing capacity.
There are 100 passengers waiting in line at an airport screening facility and they are processed at the rate of 2 per minute. Then the lead time to screen all 100 passengers is = 100/2 = 50 minutes.
Article from iSixSigma.com - http://finance.isixsigma.com/library/content/c040519a.asp One-hour recorded Webcast: "Core Process Pull: Little's Law in Action" - http://www.moresteam.com/presentations/webcast-lean-pull-systems-webcast.cfm