Lesson 1.3 — Percents

Hi again! Let's talk about percents. You see them everywhere, on sale signs, on test scores, on your phone battery. So let's really understand them.

Here's the secret: a percent is just a special ratio, out of one hundred. In fact, the word "percent" literally means "per hundred." So when you see twenty-five percent, that means twenty-five out of one hundred.

And here's the cool part. That same value can be written three ways. Twenty-five percent equals the fraction twenty-five over one hundred, which simplifies to one fourth, and it also equals the decimal zero point two five. Percent, fraction, decimal. Three outfits, same person.

Why are percents so handy? Because they put everything on one fair scale, out of one hundred. That makes different-sized things easy to compare.

Let's find a percent of a number. Say there's a forty dollar jacket, and it's twenty-five percent off. Step one, turn the percent into a decimal. Twenty-five percent becomes zero point two five. Step two, multiply by the whole. Zero point two five times forty is ten. So you save ten dollars, and you pay thirty.

What about going the other way? Suppose you got eighteen out of twenty questions right. Divide the part by the whole, eighteen over twenty, that's zero point nine, then multiply by one hundred. Ninety percent. Nice score!

And remember, one hundred percent means the whole thing. Fifty percent is half. You can even go over one hundred percent, which just means more than the whole.

Quick recap. A percent is out of one hundred. It equals a fraction over one hundred and a decimal. To find a percent of a number, turn it into a decimal and multiply. You've got this!