Percent

A percent is a way to show a part of a whole, where the whole is split into 100 equal pieces. The word comes from the Latin phrase per centum, which means "for each hundred." When you say 50 percent, you mean 50 out of every 100. The symbol for percent is %.

Percents, fractions, and decimals are three different ways to write the same idea. Half of a pizza can be written as 1/2, or 0.5, or 50%. All three mean the same amount. Percents are useful because they give every fraction the same bottom number, which is 100. That makes it easy to compare things. Saying "23% of kids" and "47% of kids" is faster than comparing 23/100 and 47/100 in your head.

To turn a fraction into a percent, you change the bottom number to 100. For example, 3/4 is the same as 75/100, which is 75%. To turn a decimal into a percent, you move the decimal point two places to the right. So 0.6 becomes 60%, and 0.08 becomes 8%.

Percents show up almost everywhere. Stores use them for sales ("30% off!"). Weather forecasts use them ("a 70% chance of rain"). Teachers use them to grade tests. Banks use them to talk about interest, which is the extra money you earn for saving or pay for borrowing. Doctors use them when talking about how often a medicine works.

A percent does not have to be smaller than 100. You can have more than the whole. If a baby panda gains weight and becomes twice as heavy as before, it has grown by 100%. If it becomes three times as heavy, that is a 200% increase. Percents can also be very small, like 0.5%, which means half of one piece out of 100.

The idea of percents is very old. Ancient Romans used taxes that worked like percents almost 2,000 years ago, before humans had even invented the modern decimal system. Merchants in Italy during the Renaissance helped make percents popular by using them in trade and banking. Today, percents are one of the most common kinds of math you will see outside of school, and knowing how to read them helps you make sense of the world.