# 7 Billion People in the World? Let’s Do the Math

The world population was expected to reach 7 billion people on Monday, according to estimates by the United Nations Population Fund.

We all know 7 billion is a lot, but how can we comprehend the enormity of this number?

Laura Jacobsen, a professor of mathematics education at Radford University, often addresses the concept of large numbers in classes in which undergraduate students prepare for careers in elementary and middle school education.

“Children and adults alike often don’t have an intuitive sense for the magnitude of large numbers, and so we try to break it down for them in ways that connect to things they do understand,” Jacobsen explained.

Grasping the enormity of seven billion can be a bit taxing to the brain, but the mathematics education professor provides a few examples to make understanding the number easier.

“If we could count each one of the 7 billion people at a rate of one person per second, without any breaks, it would take 222 years to complete the counting,” Jacobsen said.

Here is how Jacobsen made her calculation:

7,000,000,000 sec ÷ 60 sec/min ÷ 60 min/hr ÷ 24 hr/day ÷ 365 day/yr = 222 years

Easy as pi, right?

Here are a few more examples from Jacobsen to show the magnitude of 7 billion:

• If 7 billion \$1 bills were stacked, 233 bills would make an inch of thickness, and the stack would reach 475 miles or 765 kilometers high.
• End to end, 7 billion \$1 bills would wrap around the Earth’s equator more than 27 times.
• For a car with 24-inch diameter tires, if the tires rotated 7 billion times, the car would travel the distance to the moon and back more than 17 times.

Oct 31, 2011