Here's a link from Books24x7 that explains the concepts of Yield and Rolled Throughput Yield (RTY) very nicely with an example:
Chapter 5 - Crafting Insightful Metrics
Managing Six Sigma: A Practical Guide to Understanding, Assessing, and Implementing the Strategy That Yields Bottom-Line Success
by Forrest W. Breyfogle III, James M. Cupello and Becki Meadows
John Wiley & Sons © 2001 Citation
Note: You need to be a PMI Member to access the above link.