15 common math questions from the SATs everyone gets wrong

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The SAT doesn't just test how good you are at math, reading, and writing — it tests how good you are at taking the SAT.

Preparing for the math section of the test requires lots of practice and memorization of some formulas, but it's also important to know how to recognize trick questions, sift through unnecessary details, and remember simple tricks like reading the entire question through before starting to work on it.

Here are 15 math problems from the SAT that people usually get wrong — with step-by-step explanations for how to solve them.

SEE ALSO: 18 high-paying jobs for people who hate math

Many people misread this question about the original price of a laptop.

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When people read this question in a rush, they assume that it's asking about the cost of the laptop with the discount plus tax and pick "C," says SAT blog Love The SAT. But look carefully, — it's asking for the original price of the computer.

Alma is paying 8% sales tax, which can also be expressed as 108% of the price. There's also a 20% discount, meaning she's paying 80% of the price, or 0.8.

So if p is the total amount Alma paid to the cashier and x is the original price of the laptop, the equation reads as follows:

p = (1.08)(0.8)(x)

Now solve for x by dividing both sides by (1.08)(0.8).

p/(1.08)(0.8) = x

The correct answer is "D."

This question requires you to write out all the steps, even though the math itself isn't too complicated.

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You're trying to figure out the price per pound of beef (b) when it was equal to the price per pound of chicken (c). In other words, when b = c, or 2.35 + 0.25x = 1.75 + 0.40x. So you need to find the value of x in order to plug it back into the "b" equation, writes Dora Seigel of PrepScholar.

Subtract 1.75 from each side: 

2.35(−1.75) + 0.25x = 1.75(−1.75) + 0.40x

That leaves you with 0.6 + 0.25x = 0.40x. So subtract 0.25x from each side:

0.6 + 0.25x(−0.25x) = 0.40x(−0.25x)

0.60 = 0.15x

The last step is to reduce the equation:

0.60/0.15 = x

4 = x

Now that you know the value of x, you can put it into the equation for the price of beef:

b = 2.35 + 0.25x

b = 2.35 + 0.25(4)

b = 2.35 + 1

b = 3.35

The correct answer is "D," $3.35.

Here, people often solve the wrong part of the equation — a common mistake.

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This question is tricky because it gives you lots of numbers and letters and it's not entirely clear what you're supposed to do with them. It's crucial to figure out what the question is asking before you start doing pointless calculations that won't get you any closer to the answer. PrepScholar suggests reading the entire question through, circling the important information, and determining what you're being asked before doing any work.

In this case, you're looking for the value of sinF. 

Start with what you know: triangle ABC is a right triangle, and angle B is the right angle. That means that AC is the hypotenuse and BC is one of the sides.

You can use the Pythagorean theorum to figure out the length of the last remaining side:

A² + B² = C²

A² + 16² = 20²

A²  = 20² - 16²

A = √(400)−(256)

A = √144 = 12

The problem told you triangle DEF is similar to triangle ABC. That means C and F are corresponding vertices: sinF = sinC. 

If you know the acronym SOHCAHTOA, you'll know that sin = opposite/hypotenuse.

sin F = sinC = 12/20 = 3/5 = 0.6

The answer is 3/5 or 0.6.