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Beat The GMAT!

Beat The GMAT is a day-to-day blog detailing how I studied for and beat the Graduate Management Admission Test™ (GMAT). This site shall serve as a study guide for future GMAT test takers.



Day 24 - Finished Kaplan Arithmetic Chapter


This afternoon I finished the rest of the Arithmetic chapter in the Kaplan Math Workbook, pages 36-71. Like I said before, it's a slow read but very comprehensive.

One lesson that I really enjoyed in this chapter was Kaplan's strategies for thinking about averages (arithmetic means). Kaplan advocates thinking about averages as balanced values--as an example, say you have the following problem:

The average of 3, 4, 5, and x is 5. What is the value of x?

Instead of delving into time-consuming algebra to solve this problem (maybe not so time consuming with this specific problem), think about how each number is positioned relative to the average of five:

3 is 2 less than 5. (-2)
4 is 1 less than 5. (-1)
5 is the average. (0)

==> (-3)

x must be 3 more than the average to balance the set of numbers at a mean of 5. This counterbalances the -3 value created by the set of numbers given in the problem.

Thus, x = 8.

Perhaps this balancing idea is intuitive to a lot of readers out there all ready, but I've never thought of averages in this fashion. Doing so has allowed me to speed through these types of problems dramatically. Heck yes.

SUMMARY OF DAY 24 WORK:
1. Finished Chapter 2 - Arithmetic in Kaplan Math Workbook, pages 36-71.

RECAP OF DAY 24 INSIGHTS:
1. Kaplan's strategy for dealing with averages is cool.

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This entry was posted on Tuesday, May 10, 2005 at 8:32 PM. You can skip to the end and leave a response.

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Blogger Rog said at 12:52 PM

I think you meant to say: 4 is 1 less than 5, right?    



Blogger Eric said at 9:00 PM

Haha, thanks for the catch.    



Anonymous Anonymous said at 9:18 PM

Not sure how this could save time, but perhaps it would be faster:

1. Add the number of integers involved: 3, 4, 5, and x would be 4 integers.

2. Multiple your answer in step 1 with the average given (5) which would give you: 4 X 5 = 20

3. Subtract the total of the integers given (3+4+5=12) from your total in answer 2 which would give you: 20 - 12 = 8

Not sure, but these steps may prove faster.

Adam    



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