Tricky Exponents Question

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skalevar: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Wed Feb 03, 2010 5:21 pm; GMAT Score:720

by skalevar » Sun Jul 18, 2010 1:53 pm

I'm not sure how to simplify this problem:

2^x - 2^(x-2) = 3 (2^13)

What is x?

I got the question right by picking answers from the multiple choice answers, but there should have been a better way to solve. Please let me know if you have any insights.

(Correct answer is 15)

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Source: Beat The GMAT — Problem Solving | Sun Jul 18, 2010 1:53 pm

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Sun Jul 18, 2010 1:59 pm

Hi!

Like a lot of the questions you'll find from reputable sources, this one has been discussed a few times. You can find one such discussion at:

https://www.beatthegmat.com/exponent-pro ... 17726.html

The search function is very helpful - I did a search on "3(2^13)" and found the post immediately.

Good luck!

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Sun Jul 18, 2010 2:00 pm

skalevar wrote:I'm not sure how to simplify this problem:

2^x - 2^(x-2) = 3 (2^13)

What is x?

I got the question right by picking answers from the multiple choice answers, but there should have been a better way to solve. Please let me know if you have any insights.

(Correct answer is 15)

As an aside, as you note in your own post, answer choices are extremely helpful in finding the best solution to a problem. Accordingly, you should always include the choices when you post a question.

Also, if you know it, please include the source of the question.

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skalevar: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Wed Feb 03, 2010 5:21 pm; GMAT Score:720

by skalevar » Sun Jul 18, 2010 6:46 pm

The source of the question is the Practice Test 1 from mba.com. (simulated CAT test)

The answer choices were:
A. 9
B. 11
C. 13
D. 15
E. 17

Thanks for your help!

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