#### About Kevin

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!

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

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)

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.

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

Wonderful