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# OK, first post but (as all say) I have been reading for a

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VP
Joined: 11 Dec 2006
Posts: 1430
Location: New York, NY
Schools: NYU Stern 2009
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OK, first post but (as all say) I have been reading for a [#permalink]

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07 Jan 2007, 15:01
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

OK, first post but (as all say) I have been reading for a while and it has been a valuable resource. Well, also slightly intimidating, as everyone seems to have committed a lot more prep time to the GMAT than I could manage.

Anyway, I have the test tomorrow, and on the practice test only got one question that I cannot resolve. It was the first one, I got it wrong, and I can't work out the underlying process to get the answer (all the others made fair sense).

Anyway

5^21 * 4^11 = 2 * 10^n

Find n. The answers available don't really matter, I would just really appreciate a full solution so I can see what rules I am missing.
Senior Manager
Joined: 08 Aug 2006
Posts: 346
Location: San Francisco
Schools: Berkeley Haas
Followers: 4

Kudos [?]: 25 [0], given: 0

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07 Jan 2007, 15:13
4^11 = (2^2)^11 = 2^22 = 2 * 2^21

5^21 * 2 * 2^21 = 2 * (5 * 2)^21 = 2 * 10^21

n = 21

peanuts
VP
Joined: 11 Dec 2006
Posts: 1430
Location: New York, NY
Schools: NYU Stern 2009
Followers: 41

Kudos [?]: 222 [0], given: 6

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07 Jan 2007, 15:34
Thank you very much. I remember being poor at deconstructing exponentials about 12 years ago as well!

Makes good sense now - I will go back to swotting on my exponential rules.
Director
Joined: 26 Feb 2006
Posts: 901
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07 Jan 2007, 17:51
braindancer wrote:
Never argue with an idiot. They drag you down to their level, then beat you with experience.

Very touchy. I like it.

But should not it be like this "Never argue with idiots. They drag you down to their level, then beat you with their experience."?
Senior Manager
Joined: 08 Aug 2006
Posts: 346
Location: San Francisco
Schools: Berkeley Haas
Followers: 4

Kudos [?]: 25 [0], given: 0

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08 Jan 2007, 02:53
Well yes, I think you're right, but it's a quote so I left it that way

Don't overGMAT on everything - sometimes sentence correction is not really necessary
Manager
Joined: 01 Dec 2006
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10 Jan 2007, 09:10
5^21*2^22=2*2^n*5^n
5^21*2^22=2^(n+1)5^n
n+1=22 n=21
10 Jan 2007, 09:10
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# OK, first post but (as all say) I have been reading for a

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