Value of b-a from powerprep

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fightthegmat: Senior | Next Rank: 100 Posts; Posts: 31; Joined: Wed Jan 14, 2009 11:45 am; Thanked: 1 times; GMAT Score:600

by fightthegmat » Mon Sep 28, 2009 8:06 pm

If n is a positive integer,is the value of b-a atleast twice the value of 3^n - 2^n ?
1. a = 2^(n+1) and b = 3^(n+1)
2. n = 3

Source: Beat The GMAT — Data Sufficiency | Mon Sep 28, 2009 8:06 pm

tanviet: Legendary Member; Posts: 1404; Joined: Tue May 20, 2008 6:55 pm; Thanked: 18 times; Followed by:2 members

by tanviet » Tue Sep 29, 2009 6:07 am

b-a=3^(n+1)-2^(n+1)= 3.3^n-2.2^n= 3^n+2.3^n-2.2^n=3^n+ 2(3^n-2^n)

a is sufficient

b is not sufficient

farooq: Master | Next Rank: 500 Posts; Posts: 140; Joined: Sat Feb 28, 2009 8:51 am; Location: India; Thanked: 14 times; Followed by:3 members

by farooq » Thu Oct 29, 2009 3:48 am

fightthegmat wrote:If n is a positive integer,is the value of b-a atleast twice the value of 3^n - 2^n ?
1. a = 2^(n+1) and b = 3^(n+1)
2. n = 3

Please someone explain the solution of this question? It looks so hard to me.

Regards,
Farooq Farooqui.
London. UK

It is your Attitude, not your Aptitude, that determines your Altitude.

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