What makes percent problems confusing is how closely you have to pay attention to the exact words used in the problems. Anyone can use ratios to compute basic percentages; it's when problems start talking about numbers "increased by x percent" and "30 percent less than" that things spin out. So in the videos on this page I break down each of these specific wordings into steps, to show you that there's really only a few you see all the time, and that they're not so bad if you know what to look for. We'll also hit some common SAT type problems throughout, as well as in the last video, so don't think you'll never see this percent stuff again!

Percents as Ratios

In this first video we'll take a look at how to solve basic percent problems using ratios and cross multiplication. I don't recommend using this method for long, though, since I've seen so many students struggling with this percents stuff years later while preparing for the SAT, who still set up equations with x/100. Use it to learn percents, but try and move on to the decimal methods in the later videos as soon as possible!

Percent Increase & Decrease

The exact wording of percent problems is super-important, so let’s get specific! “Percent increase” and “percent decrease” are common types of problems, as well as their closely related brothers, “increased by” and “decreased by”. We’ll also cover “percent more than” and “percent less than”, mostly using decimal methods rather than ratios.

Percents As Decimals

I know I'm starting to sound like a broken record, but in this short video once again I'll pummel you about the head and shoulders with admonitions to use decimals rather than percents! And in this video, hopefully I make it look easy enough that you'll give it a try.

Hard Multi-Step Percent Problems (SAT)

When percent problems get hard, especially on standardized tests like the SAT, it's often because it's a two-step process. For example, a retail item is marked down once, then marked down again. Or, perhaps something gets bought and sold a couple times. Regardless of the exact question they're asking, the burn is always the same, and this video will show you how to always use the right denominator!

Compound Interest

Interest as in money, not interest. Compounded monthly. Compounded quarterly. Compounded semi-annually on a quarterly basis daily. The terms get confusing, but I'll get you through A=Pe^{rt} and A=P(1+e/n)^{nt} and the terminology that goes with it. And hey, you get to use your calculator!

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If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)