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 :).

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.

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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