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ACT Math Tips and Tricks

Strategy does not replace knowing the math, but it can rescue questions you would otherwise skip or miss.

Backsolve from the answer choices

When the choices are numbers, try them in the question instead of solving. They are usually listed in order, so start with the middle choice. If it is too big, move down, and if it is too small, move up.

Plug in numbers for variables

If a question is full of variables and the choices are expressions, pick easy values (2, 3 or 10, not 0 or 1), compute the target, then test the choices with the same values. If more than one choice matches, try another set of numbers.

Draw and label

Sketch the figure if there isn't one, and write every given length or angle on it. Many geometry and word problems become obvious once you can see them.

Estimate and eliminate

Rule out choices that are the wrong size or sign. A length can't be negative and a probability can't exceed 1. Even without a full solution, removing two choices improves a guess.

Use the calculator on purpose

A calculator helps with arithmetic and graph checks but does not choose the method for you. Check act.org for which calculators are allowed on your test, and practice with the one you will bring.

Read the last sentence twice

Many wrong answers are correct values of the wrong thing: the value of x when the question asks for x + 2, or a radius when it asks for a diameter. Underline what is being asked.

Never leave a blank

The ACT does not take points off for wrong answers, so answer every question. Mark hard ones, move on and fill in a guess before time runs out.

Try it

  1. What is the positive solution of x² − 5x − 14 = 0?

    • A. 2
    • B. 5
    • C. 7
    • D. 9
    • E. 14
    Show answer and solution

    Answer: C. Backsolve with the middle choice, 7: 49 − 35 − 14 = 0, so it works. (Factoring also works: (x − 7)(x + 2) = 0, so x = 7 or x = −2.)

  2. If n is an odd integer, which of the following must be even?

    • A. n + 2
    • B. 3n
    • C. n² + 1
    • D. 2n + 1
    • E. n − 4
    Show answer and solution

    Answer: C. Plug in n = 3: the choices give 5, 9, 10, 7 and −1, so only n² + 1 is even. Check with n = 5: 26, which is also even. An odd number squared is odd, and adding 1 makes it even.

For more, see the ACT Math formulas to memorize and ACT Math practice questions with answers.

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