Estimate to the order of magnitude the number of manhours re

Estimate to the order of magnitude the number of man-hours required for building the Great Wall of China. Provide explanations.

Solution

There are several Great Walls that were built by different dynasties such as the Qin Great Wall and the better known Ming Great Wall. In all, many imperial dynasties and kingdoms built, rebuilt, and extended walls many times in a period of more than 2000 years.

The latest imperial construction was performed by the Ming Dynasty (1368–1644), and the length was then over 6,000 kilometers (3,700 miles). This is the wall often referred to when we talk about \"the Great Wall\". If we just estimate about 500,000 laborers working 10 hours a day for perhaps 6 days a week and rounding off to 50 weeks a year and for a period of 200 years, we\'d have an estimate for the number of man-hours.

0.5 million x 10 x 6 x 50 x 200
= 300,000 million
= 300 billion man-hours.

But if you wanted to estimate the total time spent constructing all the prior sections and rebuilt sections over the 2000 year period of wall construction, it would be even larger than that.