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tj123: Senior | Next Rank: 100 Posts; Posts: 85; Joined: Mon Dec 08, 2008 12:09 am

by tj123 » Sat Jul 25, 2009 5:42 pm

what is the value of 10^(x+1) * 7^(y-1)?

1) 1o^x * 7^y = 2401

2) x+y=4

Please explain

OA A

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Source: Beat The GMAT — Data Sufficiency | Sat Jul 25, 2009 5:42 pm

prax_us: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Thu May 21, 2009 2:49 am

by prax_us » Sat Jul 25, 2009 7:49 pm

10^x+1 => 10*(10)^x
7^y-1 => (7^y)/7
=> (10^x*7^y)*10/7 - A will substitue the value

B has variable results. Thus A is sufficient.

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