Math CentralQuandaries & Queries


Question from Kenneth:


When a decimal or a number is changed to a percent, the decimal or number is multiplied by 100 and then a percent sign (%) is attached.
Why is it necessary to multiply by 100?
What is the reasoning or logic for using this calculation?

I thank you for your reply.

Nice question! Never take things for granted.

To be specific, this what we do when a fraction or decimal expressing a portion of ONE unit is changed to a percent. It's not what we'd do if we were changing (say) 5g of water in 500g of margarine, or 0.05 liters of alcohol in 0.5 liters of wine, or three eggs in a dozen.

Now, "percent" means "(parts) per hundred" ("centum" in Latin) so 50% means "fifty parts per hundred," etc. The percent sign is just that - a sign meaning "parts per hundred."

So, to scale from "amount per 1 unit" to "amount per 100 units" we multiply by 100. And we add the percent sign to show we've done it.

Good Hunting!

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