DS INTEGER

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[email protected]: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Sun Jul 24, 2011 10:36 am

DS INTEGER

by [email protected] » Thu Sep 22, 2011 8:13 am

Q: IF M AND N ARE INTEGERS, AND X= 3^N AND Y= 3^M .IS X >2Y ?

A: N= M+1
B: N= 2M

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Source: Beat The GMAT — Data Sufficiency | Thu Sep 22, 2011 8:13 am

gmatclubmember: Master | Next Rank: 500 Posts; Posts: 158; Joined: Sat Sep 03, 2011 10:31 am; Thanked: 29 times; Followed by:2 members

by gmatclubmember » Thu Sep 22, 2011 8:24 am

[email protected] wrote:Q: IF M AND N ARE INTEGERS, AND X= 3^N AND Y= 3^M .IS X >2Y ?

A: N= M+1
B: N= 2M

Consider A:
x>2y=> 3^n > 2.3^(n-1) => 3^n > 2/3 * 3^n ---- sufficient.
Consider B:
x>2y => 3^2m > 2.3^m => insufficient.

So answer is A.

Cheers
Ami/-

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cans: Legendary Member; Posts: 1309; Joined: Mon Apr 04, 2011 5:34 am; Location: India; Thanked: 310 times; Followed by:123 members; GMAT Score:750

by cans » Thu Sep 22, 2011 8:29 am

X= 3^N AND Y= 3^M . IS X >2Y ??
3^n > 2*3^m ??
A) n=m+1. thus lhs = 3*3^m. as 3>2 sufficient
B) n=2M.
3^(2m) > 2* 3^m ?? or 3^m * 3^m > 2*3^m or 3^m>2???
if m=0, 1>2 false
if m=1, 3>2 true
Insufficient
IMO A

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[email protected]: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Sun Jul 24, 2011 10:36 am

by [email protected] » Thu Sep 22, 2011 11:33 pm

cans wrote:X= 3^N AND Y= 3^M . IS X >2Y ??
3^n > 2*3^m ??
A) n=m+1. thus lhs = 3*3^m. as 3>2 sufficient
B) n=2M.
3^(2m) > 2* 3^m ?? or 3^m * 3^m > 2*3^m or 3^m>2???
if m=0, 1>2 false
if m=1, 3>2 true
Insufficient
IMO A

THANKS FOR YOUR POST.
BUT WE DON'T KNOW THAT BOTH M AND N ARE POSITIVE OR NEGATIVE INTEGER. IF BOTH ARE NEGATIVE THAN I THINK THE ANSWER WOULD BE NOT SAME AS WHEN BOTH ARE POSITIVE