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# GMAT Tuesdays: Data Sufficiency – Watch Your Assumptions!

Don’t get caught assuming too much on the GMAT. They are looking for students to make big assumptions when they are trying to save time.

In this Data Sufficiency question, there is a big trap for anyone who assumes too much about the problem.

This week’s board:

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### 5 Responses to GMAT Tuesdays: Data Sufficiency – Watch Your Assumptions!

1. Mahmoud Ahmed February 24, 2017 at 10:26 am #

Hello but why we can’t replace x with y from the second equation like this:

5x+3(5-5/3x)=15
5x+15-14x=15
-9x+15=15
-9x=0
x=0

• Magoosh Test Prep Expert February 25, 2017 at 8:38 am #

Hi Mahmoud,

The problem is that both equations are exactly the same, but written slightly differently. So, you cannot plug in an equation into itself. Let me prove it! The reason you got an answer above is that there was a slight careless error in your calculations.

5x + 3(5-(5/3)x) = 15 [Distribute the “3”]
5x + 15 – 5x = 15 [Combine like terms]
15 = 15

This does not prove anything. This happened because we used an equation on itself! I hope this helps! 😀

2. Sam July 11, 2016 at 8:13 pm #

This is fantastic.

I keep falling for this.

Thanks for this lesson

3. sonal July 23, 2015 at 9:29 am #

sir how to join the events that you conduct ..?

• Kevin Rocci July 23, 2015 at 9:59 am #

Hi Sonal! 😀

The videos I record are not live events. I record them in advance and publish them every Tuesday. Sorry that there isn’t an event for you to join. 🙁 I hope you like the videos, though! 😀

Happy Studying!

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