3 Most Common Mistakes You Want to Avoid On the ACT Math Section

Veritas Prep ACTThe ACT Math has one major advantage compared to the ACT English and Reading portions: no “best answer” choices. Instead, there will be only one possible, objective, absolute correct selection to make. So if your calculator spits out a number that isn’t A, B, C, D, or E, you know you need to re-do your math.

If you’ve taken algebra and geometry classes in your high school career, you will know 99% of the content of the exam. The trick is avoiding simple errors in your calculations that also yield a multiple choice answer. The following is an example excerpted from a sample math question on the ACT website:


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This is a simple solve-for-x scenario that most ACT Math test-takers are familiar with. Note the answer choices.


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With both sides of the equation balanced properly, the correct answer is E.


Say, for instance, that a student who knew how to balance equations accidentally added three instead of subtracting 3 to one side. The answer yielded, “1,” is among of the multiple choice. C.


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In this way, the multiple choice selections for the majority of the ACT Math portion rely on students making errors in basic operations. Below are a few of those common errors:


  1. Distributing the Negative

-2(x+2) does NOT equal -2x+4.

-2(x+2) = -2x 4.

It’s a simple rule, but always be wary of negative signs on the ACT Math.

  1. Square Roots:

The square root of 64 is 8. But it’s not the *only* square root. -8 is the other.

This detail is especially important on questions that concern quadratic functions or ask for the “number of possible solutions.”        

  1. Percent Change:

Take the given, simplified example: “A $100,000 investment grows by 50 percent in the course of 2015.=

What is it’s new value in 2016?”

Too many students will solve this question using the equation below:

100,000 x .50 = $50,000

Whenever calculating new value in a percent growth problem, the solution must be higher than the original value.

100,000 x 1.50 = $150,000   ==> This is correct.

The new value = $150,000.

The difference = $50,000.

As always, if time allows, the most valuable strategy is to check your answers before proceeding to the next problem. A quick calculation to make sure that your multiple choice selection satisfies the conditions and equations of the original question will catch most of these errors!

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Madeline Ewbank is an undergraduate at Northwestern University in Evanston, IL, where she produces student films, interns for the Department of State, and teaches ACT 36 courses. She is excited to help students achieve their college aspirations as a member of the Veritas Prep team.