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GMAT Tuesdays with Kevin: Percent Change Trap, Part 2

UPDATE: We replaced the old GMAT Tuesday in this post with a new video because one of our readers spotted an error and brought it up to us–thank you, Alex!

This week is a continuation of last week’s GMAT Tuesday video! I’ll show you how to solve that tricky percent change problem faster with a little help from multipliers.

Leave me a comment or question below! It’d really make my day :).

About the Author

Kevin has taught for over ten years from San Francisco to Japan, helping students prepare for tests, like the GRE, GMAT, and SAT. He enjoys sharing what he learned, so even more students can achieve their goals. When he is not helping students dominate standardized tests, you can find him in the Pacific Ocean or on a granite dome in the Sierra Nevada Mountains. Follow him on Google+ and on Twitter @KevinRocci!

6 Responses to GMAT Tuesdays with Kevin: Percent Change Trap, Part 2

  1. Alex July 11, 2014 at 1:27 pm #

    Does the above always work though? For example, let’s say the suit increased in price by 50% and then I walked in with a 20% off coupon (off the increased price). The formula you provided would suggest that I do: $200 * (1 + (0.5)*(-0.2)) –> $200 * (1-0.1) –> $200 (0.9) –> $180. However, the actual math would be $200 * 1.5 = $300 –> $300 * (0.8) = $240

    • Alex July 11, 2014 at 1:30 pm #

      I think the up and down 30% hides the fact that you’re doing a difference of squares formula, i.e. (1+0.3) * (1-0.3) = 1 – 0.09, i.e. 1+ (0.3)(-0.3). If the two figures were different, you’d have to do 1.3 * 0.7 vs. the shortcut of just (0.3)(-0.3)

      • Kevin
        Kevin July 16, 2014 at 5:54 pm #

        This is 100% correct! I have made a big mistake at the end of this video and did not multiply our multipliers together. I multiplied our decimals together.

    • Kevin
      Kevin July 16, 2014 at 5:53 pm #

      You are 100% correct! Alex your points are true and correct. We are going to need to re-record this video.

  2. tvm27 February 22, 2014 at 5:50 pm #

    Wonderful :)

    • Kevin
      Kevin February 23, 2014 at 11:29 am #

      :)


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