Tips for Taking the Mathematics Knowledge Subtest of the ASVAB - dummies

Tips for Taking the Mathematics Knowledge Subtest of the ASVAB

By Rod Powers

For most people, scoring well on the Mathematics Knowledge subtest requires more than just showing up on time and borrowing a No. 2 pencil and piece of scratch paper. Maybe you’ll breeze through without a problem. Or, maybe you’ll get stuck on a question or run into other roadblocks. When this happens, having a plan of attack is helpful.

Keep an eye on the all-important clock

Like all subtests of the ASVAB, the Mathematics Knowledge subtest is timed. If you’re taking the paper test, you have just 24 minutes to try to correctly answer 25 questions. That’s 57.6 seconds per question. The room will have a clock in it, and the start time and stop time will be posted somewhere in the room, easily visible to you and the other test takers.

If you’re taking the computerized version of the ASVAB, you get 16 questions in 20 minutes, and your remaining time will be shown in the upper corner of your computer screen.

Keep an eye on the clock. You want to try to finish the test before time runs out. Try to average about 45 or 50 seconds per question.

Double your chances by double-checking

If you have time, double-check your answers. Those crafty test makers often provide wrong answer choices that work if you made a common error, so don’t assume that your answer is the right one just because it matches one of the possible answer choices. Look at the following example:



  • (A)1/8

  • (B)2

  • (C)17

  • (D)1/2

To correctly solve this problem, you multiply the first fraction by the reciprocal (flipped over) value of the second fraction:


So the correct answer is Choice (D), 1/2. If you multiplied the fractions instead of dividing, you would’ve gotten Choice (A). If you took the reciprocal of the first fraction rather than the second, you would’ve gotten Choice (B). If you took a wild guess, you might’ve gotten Choice (C).

Although double-checking your answers is always a good idea, remember to keep an eye on the clock. You don’t want to run out of time with only half the questions answered because you’ve spent too much time double-checking all your answers.

Use the answer choices to your advantage

If you’re stuck on a particular problem, sometimes plugging the possible answer choices into the equation can help you find the right answer.



(A) 25

(B) 50

(C) 100

(D) 75

The right answer is Choice (C), 100. What can you do if you get stuck? You can replace x in the equation with the known possible answer choices and see whether any of them work.

First, recognize that you can simplify the equation to


by adding 45 to both sides. Now start substituting the answer choices for x:

  • x = 25:


    That doesn’t work.

  • x = 50:


    That certainly doesn’t work.

  • x = 100:


    You can stop here because Choice (C) is the correct answer.

Don’t forget that plugging in all the answers is time-consuming, so save this procedure until you’ve answered all the problems you can answer. If you’re taking the computer version, you can’t skip a question, so remember to budget your time wisely; if you don’t have much time, just make a guess and move on.

Playing the guessing game

Guessing incorrectly on any of the paper ASVAB subtests doesn’t count against you. So fill in an answer — any answer — on your answer sheet because if you don’t, your chances of getting that answer right are zero. But if you take a shot at it, your chances increase to 25 percent.

If time is running short on the CAT-ASVAB, try to read and legitimately answer the questions rather than filling in random guesses for the remaining items. The CAT-ASVAB applies a relatively large penalty when you provide several incorrect answers toward the end of the subtest.

If you’re taking the paper version of the ASVAB, you can always skip the tough questions and come back to them after you’ve finished the easier ones. If you’re taking the computerized version of the ASVAB, the software doesn’t let you skip questions.

If you’re taking the paper version of the test and elect to skip questions until later, make sure you mark the next answer in the correct space on the answer sheet. Otherwise, you may wind up wearing out the eraser on your pencil when you discover your error at the end of the test.

Sometimes you may know how to solve part of a problem but not all of it. If you don’t know how to do all the operations, don’t give up. You can still narrow your choices. Suppose this question confronts you:

What is the value of (–0.4)3?

  • (A)–0.0027

  • (B)–0.000064

  • (C)0.000064

  • (D)0.0009

What if you don’t remember how to multiply decimals? All is not lost! If you remember how to use exponents, you’ll remember that you have to multiply


So if you simplify the problem and just multiply


without worrying about those pesky zeros, you know that your answer will be negative and will end in the digits 64.

With this pearl of wisdom in mind, you can see that Choices (A), (C), and (D) are all wrong.