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prithviforever: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Sun Mar 20, 2011 8:44 am; Thanked: 1 times

by prithviforever » Sat Jul 09, 2011 9:53 am

if 2^x - 2^(x-2) = 3(2^13), what is the value of x
1.9
2.11
3.13
4.15
5.17

Source: Beat The GMAT — Problem Solving | Sat Jul 09, 2011 9:53 am

amit2k9: Master | Next Rank: 500 Posts; Posts: 461; Joined: Tue May 10, 2011 9:09 am; Location: pune; Thanked: 36 times; Followed by:3 members

by amit2k9 » Sat Jul 09, 2011 10:10 am

2^x(1-1/4) = 3(2^13)
2^(x-2) * 3 = 3 (2*13)

thus x-2=13; x=15.

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goalevan: Master | Next Rank: 500 Posts; Posts: 111; Joined: Tue Dec 30, 2008 1:25 pm; Location: USA; Thanked: 28 times; GMAT Score:770

by goalevan » Sat Jul 09, 2011 10:32 am

2^x - 2^(x-2) = 3 * 2^13
2^(x-2) * (2^2 - 1) = 3 * 2^13
2^(x-2) * (3) = 3 * 2^13
2^(x-2) = 2^13
x - 2 = 13
x = 15

D

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