Percents are a specific type of fraction. Percent literally means “of 100” in Latin, so after you ace the SAT, go to college, drop out to become famous, and eventually amass 75 percent of all the money in the world. You’ll then have ⁷⁵ /₁₀₀ of the world’s money. Awesome.

Until then, you don’t have that much money, and you still have to take the SAT (and pay for the privilege). So let’s look at an example question:

The first thing you have to know how to do is translate this sort of question into an equation. It’s actually pretty straightforward as long as you see that “is” is the same as saying “equals,” and “what” is the same as saying “x.” So if 4 equals x percent of 20, then

Since a percent is actually a number out of 100, this means

Now just work out the math:

Therefore, 4 is 20% of 20.

Converting percents into fractions or decimals is a crucial SAT skill. If you ever want to multiply or divide a number by a percent, you first have to convert it.

SAT word problems often seem to be phrased as if the person who wrote them doesn’t know how to speak English. The SAT does this purposefully, because it thinks that verbal tricks are a good way to test your math skills. If that makes no sense to you, good. It makes no sense to us either. Here’s an example of the kind of linguistic trickery we’re talking about:

Because the 2 is the smaller number and because it appears first in the question, you’re first instinct may be to calculate what percent 2 is of 5.

But as long as you remember that “is”means “equals” and “what” means “x” you’ll be able to correctly translate the word problem into math:

So 5 is 250% of 2.

One of the most common ways the SAT tests percent is through the concept of percent increase and decrease.

One of the classic blunders students make on these questions is to figure out what the 10% increase or decrease is, but then, lost in a haze of joy and relief, to forget to carry out the necessary addition or subtraction. SAT traps take advantage of this. Be wary.

First find the price decrease (remember that 15% = .15):

Now, since the price of the shirt was less back in the 1970s, subtract $3 from the $20 price from the early 1990s:

The answer is B. If you only finished the first part of this question and looked at the answers, you might see the $3 at answer A and forget to finish the calculation.

Some SAT questions ask you to determine a percent of a percent.

This question asks you to determine the effect of two successive percent changes. The key to solving it is realizing that each percentage change is dependent on the last. You have to work out the effect of the first percentage change, come up with a value, and then use that value to determine the effect of the second percentage change.

When you’re working on a percentage problem that involves a series of percentage changes, you should follow the same basic procedure that we explained for one percentage change, except here you should run through the procedure twice. For the first percentage change, figure out what’s the whole, calculate the percentage of the whole, make sure to perform addition or subtraction if necessary, then take the new value and put it through these same steps for the second percentage change.

To answer the example problem, first find 25% of the original price:

Now subtract that $.50 from the original price:

Then increase $1.50 by 10%:

Sam buys the banana for $1.50 + $.15 = $1.65. A total rip-off.

Some students, sensing a shortcut, are tempted to just combine the two percentage changes on double percent problems. This is not a real shortcut. It’s more like a dark alley filled with cruel and nasty people who want you to do badly on the SAT.

If you reasoned on the last example problem that the first percentage change lowered the price 25% and the second raised the price 10%, meaning that the total change was a reduction of 15%, then

Subtract that $.30 from the original price:

We promise you that when the SAT gives you a double-percent problem, it will include this sort of wrong answer as a trap among the choices.