Magoosh Test Prep ExpertFebruary 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.

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! 😀

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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

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! 😀

This is fantastic.

I keep falling for this.

Thanks for this lesson

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

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!