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by f2001290 » Sat May 26, 2007 5:11 am
If n is a positive integer,is the value of b-a at least twice the
value of 3^n - 2^n
(1) a = 2^n+1 and b=3^n+1
(2) n =3
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Source: — Data Sufficiency |
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by Cybermusings » Sun May 27, 2007 1:52 am
Statement II is clearly insufficient since it mentions nothing about either a or b.

Statement I: says that b= 3^ (n+1) and a = 2^ (n+1)…
Now with the law of exponents we know that 3^n+1 can also be written as 3^n * 3. Likewise 2^n+1 can be written as 2^n * 2.
Hence b-a = (3^n * 3) – (2^n *2) ---- 1)
2 times (3^n – 2^n) = (3^n*2) – (2^n * 2) ----- 2)
Clearly 1) is more than 2)….Hence sufficient

Answer should be A
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