Percents

What is interest?

Interest is a percentage rate that is paid on borrowed money.

Sometimes, that interest is paid by a person to a lender or bank (when that person borrows money).

Other times, that interest is paid to a person by a lender or bank (when that person deposits money that the bank can then lend to other people).

When someone borrows or deposits money, they are given an interest rate (usually in percentage form).

The amount that they borrow or deposit is called the principal.

What is a commission?  People earn a commission when they earn a percentage of what they sell.  Many professionals (e.g., realtors, salespeople, mortgage brokers, etc.) work on commission. Every time they make a sale, they get some percent of the sale prices as their salary. That percentage that they earn is a commission.

How do you calculate a commission?  

Someone might say that his commission is 4% of the sales price.  

Although it's not at all hard to increase or decrease a number by a percent (review the Percent Increase/Decrease lesson if this doesn't sound familiar), it can be tricky to find the percent a number was increase or decreased by.

Finding a percent of a number means finding a part or portion of a number. Increasing/decreasing a number by percent means finding a percent of a number and adding or subtracting that amount from the original number. We deal with percent increases (mark-ups, tips, sales tax) and decreases (sales, discounts) all the time. Calculating percent increases and decreases mostly involves finding a percent (if you need to review that, review the Finding a Percent lesson) and then adding it to, or subtracting it from, your original number. 

Percents are one of the types of math that we use the most in real life, which is probably why they lend themselves so nicely to word problems!

If you know how to find percents from all different angles (see our Percents Lessons), word problems are easy.  You can use a simple formula, or a proportion, fill in the items you know from the word problem, and solve.

Remember, "of" means multiplication in math.

Sometimes you are given a percent and a number, and asked to find the whole number that that percent is based on.  

There are several ways to find a whole number based on a percent.  EdBoost's preferred way to to use a proportion (not necessarily because it's the easiest way to do this operation, but because there are several related operations, and using a proportion makes it clear how to solve all kinds of percent problems).

Example: 20 is 80% of what number?

Finding a percent of a number means finding a part or portion of a number. A percent is another way to write a decimal or a fraction, so finding a percent of a number is the same as finding a fraction or decimal of a number. One great math rule to remember: the word "of" means multiply in math.

Finding a percent based on a portion of a number means figuring out what percent a specific portion represents.  When thinking about percents, remember that percent means "per 100" (think, per (each) and cent (100 as in century)).  Remember that portions do not have to be written as percents.  They can also be written as decimals or fractions (which are fairly easily converted to percents).  So 15% can also be written as .15 or $\dfrac{15}{100}$.