More Confusion with Percentages

As I’ve shown in one or two previous posts, people use the word percentage in a very casual way. That is, they use it incorrectly. I won’t reiterate the details, but here’s another example from one of my favorite technical websites – a website that should know better.

In an article on the age of the earth they write: “It may be some time before we can answer all these questions, but really, we’ve made pretty good progress-we’ve only been at it for 0.0000001 percent of the Earth’s existence.”

In the article they give the earth’s age as 4.55 billion years, and they say that serious investigations of this age have been going on “only in the last couple centuries“. Since they came up with a nice tidy percentage they were probably using 455 years as the numerator, and 4.55 billion years as the numerator. The standard formula for percentage is:

Percentage = 100 * numerator / denominator

Working that out with my trusty calculator (to avoid any careless mistakes) I get:

100 * 455 / (4.55 * 1,000,000,000) = 0.00001%

That number doesn’t match the number from the article summary. My number is exactly 100 times larger. As is very common they have calculated the ratio of the two numbers and called it a percentage, without actually making it a percentage.

Dividing two numbers gives you a ratio. Multiplying by a hundred gives you a percentage. If you simply stick the percentage label on a ratio then you are off by a whopping two orders of magnitude!

The other possibility is that I misinterpreted their calculation. If they actually meant to say that we have only been able to seriously investigate the age of the earth during the last 4.55 years then their math is correct and I apologize.


It’s fixed. If only getting the NHL and Mythbusters to change their ways was so easy.

About brucedawson

I'm a programmer, working for Google, focusing on optimization and reliability. Nothing's more fun than making code run 10x as fast. Unless it's eliminating large numbers of bugs. I also unicycle. And play (ice) hockey. And sled hockey. And juggle. And worry about whether this blog should have been called randomutf-8. 2010s in review tells more:
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