# GMAT Errors: Avoid Face-Palm Moments

June 25, 2012 by

How many times have you reviewed a question that you missed in practice and had that “face-palm” moment in which you realize that you missed something because you stopped too soon or solved for the opposite or just a portion of what the question was asking for? It happens too many times for most test-takers. So many of the mistakes made on the GMAT are avoidable errors. This is especially true on the simpler quantitative problems, because test-takers commonly let their guard down on the easier problems. They take the moment to breathe and end up walking straight into an easy error even though they understand the concept being tested.

Take this question for example:

There are 84 supermarkets in the FGH chain. All of them are either in the US or Canada. If there are 22 more FGH supermarkets in the US than in Canada, how many FGH supermarkets are there in the US?

a. 20

b. 31

c. 42

d. 53

e. 64

There are two variables in this word problem, US supermarkets and Canadian supermarkets. First, many people default to “X” and “Y” as standard variables; however, if it is possible, strive to pick variables that better represent the items in the question because “X” and “Y” are easily confused at the end of the question and can easily lead to the “face-palm” answer choice. Let’s avoid that possibility here by using U and C as we translate the two equations in this word problem. As Lucas has mentioned previously, be systematic about how you unpack a word problem.

“There are 22 more FGH supermarkets in the US than in Canada.”

U = 22 + C

Also, “there are 84 supermarkets in the FGH chain.”

U + C = 84

Here’s how one could understand the math but still easily miss this question. Because the first equation already has “U” isolated, most test-takers will substitute that directly into the 2nd equation. While this is mathematically legal, immediately taking the most obvious and familiar route before thinking carefully about where you are headed in order to solve for US supermarkets leads right to the “face-palm” answer choice that is lying in wait.

(22 + C) + C = 84

22 + 2C = 84

2C = 62

C = 31

This seems fairly simple mathematically, and answer choice “B” is sitting there as a possibility; however, it’s not the answer to the actual question. Answer choice “B” represents the number of Canadian supermarkets instead of the asked for US supermarkets.  You can see how this could be especially confusing if we were using just “X” and “Y” as the variables.

To avoid this potential situation with two variables, it’s usually best either to use combination if you are going to do the math or to backsolve starting with answer choice B or D as the number of US supermarkets.

In combination, we would want to make sure that the “C” can cancel out, leaving us with the desired “U” at the end.

U – C = 22 (first equation rearranged in line with the second equation)

+ ( U + C = 84)

2U = 106

U = 53, which is the correct answer

Let’s take a look at one more in which a simple problem can easily go awry if you don’t stay on your toes.

The officers of a local charity met together to address 500 invitations to an upcoming fundraising event. If they addressed 1/5 of the invitations in the first hour, and 3/8 of the remaining invitations in the second hour, how many invitations remained to be addressed after the first two hours?

a. 100

b. 150

c. 250

d. 350

e. 400

As you work toward the asked for number of invitations left to be addressed after two hours, all of the answer choices in this question are numbers that you could get using the information in the question.

(1/5)500 = 100 –> the number addressed in the first hour and incorrect answer choice A

500-100 = 400 –> the number remaining after one hour and incorrect answer choice E

(3/8)400 = 150 –> the number addressed in the second hour and incorrect answer choice B

500 – 150 = 350 –> the number remaining if you only take hour 2 into consideration and incorrect answer choice D