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urban population

Urban Careers and the Twenty-Ninth Day

Dan Hoornweg's picture

Lily pads on lakeA helpful way for young math students to grasp the concept of exponential growth is to look at water lilies growing on a pond. They grow exponentially and double in area each day. If they will fully cover the pond by the 30th day, on what day is the lake half covered? The twenty-ninth day[1].
 
This year I had the honor of teaching 4th year energy systems students who will graduate later this month (their blogs on energy issues will be presented on this site over the summer). These graduates are particularly essential. During their careers they will be part of the world’s largest ever city-building spree. Their task will be to again double the world’s cities.