Download or read book The Twenty-ninth Day written by Lester Russell Brown and published by W. W. Norton. This book was released on 1978 with total page 363 pages. Available in PDF, EPUB and Kindle. Book excerpt: A lily pond, so the French riddle goes, contains a single leaf. Each day the number of leaves doubles--two leaves the second day, four the third, eight the fourth, and so on. Question: If the pond is completely full on the thirtieth day, when is it half full? Answer: On the Twenty-ninth day.