GMAT prep exponent question

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unc42: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Tue Jul 22, 2008 2:29 pm

by unc42 » Sat Aug 09, 2008 6:44 am

I couldn't find this posted yet, so I apoligize if this has been asked before...

5^21 x 4^11 = 2 x 10^n solve for n

answer is n=21, I'm not sure how to get there.

Thanks for any help!

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Source: Beat The GMAT — Problem Solving | Sat Aug 09, 2008 6:44 am

bourne159: Senior | Next Rank: 100 Posts; Posts: 50; Joined: Tue Mar 11, 2008 6:30 am; Thanked: 6 times

by bourne159 » Sat Aug 09, 2008 7:19 am

5^21 x 4^11 = 2 x 10^n solve for n

answer is n=21, I'm not sure how to get there.

5^21 x 4^11= 5^21 x (2^2)^11= 5^21 x 2^22

2 x 10^n = 2 x (5x2)^n=2 x 5^n x 2^n=5^n x 2^n+1

Therefore 5^21 x 2^22 = 5^n x 2^n+1
You can see n = 21

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