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gmat prep exponent question

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gmat prep exponent question

by xcise_science » Mon Nov 26, 2007 9:08 pm
Someone posted this question before, but I can't find it on the forums, can someone explain it?

5^21*4^11=2(10^n), what is n?


Thanks
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by syv11 » Mon Nov 26, 2007 9:25 pm
5^21*4^11=2*10^n
5^21*(2^2)^11=2*10^n
5^21*2^(2*11)=2*10^n
5^21*2^22=2*10^n
5^21*2^21=10^n
10^21=10^n
n=21
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by xcise_science » Tue Nov 27, 2007 6:48 am
thanks, but how did you get from here:
5^21*2^22=2*10^n to
5^21*2^21=10^n
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by sujaysolanki » Tue Nov 27, 2007 6:55 am
2^22 - 2^1 is what being used ...
that gives 2^21 ..then the powers can be combined a ^x * b ^ x = ab ^x
hope that helps
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by xcise_science » Tue Nov 27, 2007 8:38 am
oh, ok, so you subtracted 2 from both sides?
I didn't see that before.

Thanks!
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by syv11 » Tue Nov 27, 2007 9:14 am
You need to devide it by 2! Not substract!

2^22/2 = 2^(22-1) = 2^21
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