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David Recine

ACT Math Multiple Choice Strategies


There are two basic multiple choice test strategies that will always work on the ACT: eliminating answers that aren’t supported by the information given and eliminating answers that create mistakes. An answer creates a mistake if it introduces an error into the process for writing, calculating, or inferring information.

Eliminating Incorrect Answers on ACT Math

ACT Math tends to test your ability to do all of the steps of a math problem correctly. As a result, the second strategy I mentioned, detecting mistakes in the answers, is effective on most of the multiple choice questions in the Math section.

Here is a math question where eliminating mistakes can really help:

A room has a square floor plan that measures 15 by 15 ft. A doorway takes up 20% of the 15 feet on one side of the room. If there is wood trim along the edge of the floor everywhere except the doorway, approximately how many total feet of wood trim does the room have along the edge of the floor?

In ACT Math, the idea behind eliminating mistakes is to catch your own potential mistakes in math calculations. So the first thing you’ll want to do for this problem is calculate it yourself.

A square floor plan that is 15 by 15 feet would have four 15-foot sides for a total of 60 feet of floor edge. To know how many feet of wood trim are along that edge, you’ll need to subtract the width of the doorway, since there’s no wood trim in that part of the room. The doorway takes up 20% of one 15 foot side of the room. 20% equals 2/10, which can be simplified 1/5. So the width of the doorway will be 1/5 of 15, or 3. 60 minus 3 is 57, so there are 57 feet of word trim along the edge of the floor in this room.

57 can be selected from the answer choices below:

A) 54
B) 57
C) 58
D) 63
E) 65

To make sure you really did arrive at the answer of 57 correctly, check the other answers to see if they’re derived from any obvious mistakes. 54 is what you get what you subtract 6 from 60, which is double the 3 you should subtract. You could make this mistake if you accidentally converted 2/10 into 2/5 rather than 1/5. (2/5 of 15 is 6.) 58 is what you get when you subtract 2 from 60—this can happen if you accidentally drop the 10 from the fraction 2/10, turning it into just 2.

Next come D and E. Both of these answers stem from the same basic error: adding to 60 rather than subtracting from it, either by adding 3 when you should subtract 3, or accidentally expressing 1/5 as just 5 and then adding it to 60 instead of subtracting.

If you really did calculate the correct answer the very first time, screening for answers that stem from math missteps isn’t necessary. However, miscalculations are common, especially under timed testing conditions where test-takers struggle to focus due to test anxiety (and sometimes math anxiety as well).

The first strategy I mentioned at the beginning of this post, avoiding answers that aren’t reflected in the information given, is a less commonly useful strategy in ACT Math, but it still can be used in some cases. It’s especially important to make sure each answer is supported by data when you’re presented with a geometric figure, coordinate plane, information table, or other data. Always make sure to avoid giving answers that are not shown in a prompt or are impossible based on the pattern established in the math question.


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About David Recine

David is a test prep expert at Magoosh. He has a Bachelor of Social Work from the University of Wisconsin-Eau Claire and a Masters in Teaching English to Speakers of other Languages from the University of Wisconsin-River Falls. He has been teaching K-12, University, and adult education classes since 2007 and has worked with students from every continent. Currently, David lives in a small town in the American Upper Midwest. When he’s not teaching or writing, David studies Korean, plays with his son, and takes road trips to Minneapolis to get a taste of city life. Follow David on Google+ and Twitter!

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