ds -ve integer

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Thu Jan 20, 2011 5:54 am

If m and n are negative integers, what is the value of (mn)?
(1) m^n = 1/81
(2) n^m =-(1/64)

i doubt for B...Oa is B..

pl explain your choice.

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Source: Beat The GMAT — Data Sufficiency | Thu Jan 20, 2011 5:54 am

jaxis: Master | Next Rank: 500 Posts; Posts: 101; Joined: Sun Sep 26, 2010 9:33 am; Thanked: 5 times

by jaxis » Thu Jan 20, 2011 6:42 am

N^M = -(1/64)

N=-4
M=-3

or

N=-64
M=-1

B cant be the OA.

It shud be C

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aleph777: Master | Next Rank: 500 Posts; Posts: 131; Joined: Fri Jun 18, 2010 10:19 am; Location: New York, NY; Thanked: 10 times

by aleph777 » Thu Jan 20, 2011 8:19 am

The clue to the answer here is that the original question states that both M and N are negative numbers. Therefore, right of the bat, we know that negative * negative = positive, but positive * negative = negative.

Statement 1 is INSUF because you can reach 1/81 two ways:
-9^-2 (which is negative * negative) OR -3^-4 (which is negative * negative * negative * negative)

Statement 2 is SUF because there's only one combination that will yield a -(1/64):
-8^-2 = 1/64 BUT -4^3 = -(1/64)

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AIM GMAT: Legendary Member; Posts: 857; Joined: Wed Aug 25, 2010 1:36 amFollowed by: 15 members; Thanked: 56 times

by AIM GMAT » Thu Jan 20, 2011 8:36 am

Wow !! Thanks aleph777 and jaxis as well as advita for this question , i also went with C .Now i know where i was mistaken . Silly makes me go crazy .... i will keep this in mind .

Thanks & Regards,
AIM GMAT

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Thu Jan 20, 2011 7:53 pm

hi guys... thanks all.
but i still doubt how it is B.

Q:If m and n are negative integers, what is the value of (mn)?
(1) m^n = 1/81
(2) n^m =-(1/64)

as jaxis told:
2. consider n=-4 m=-3 so n^m=-1/64. ==> mn=12
if n= -64, m= -1, so n^m=-1/64 ==> mn=64.

so how it can be B.
1. m=-9,n=-2 or m=-3 , n=-4

so isn't it should be E.

pl confirm. thanks.

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aleph777: Master | Next Rank: 500 Posts; Posts: 131; Joined: Fri Jun 18, 2010 10:19 am; Location: New York, NY; Thanked: 10 times

by aleph777 » Fri Jan 21, 2011 6:49 am

ohhhhh... i see what you're saying. that is weird. i'm not sure, then. it would seem you'd need to pick C after all.

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samrendra4u: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Wed Aug 25, 2010 8:09 pm

by samrendra4u » Fri Jan 21, 2011 8:00 am

advita wrote:If m and n are negative integers, what is the value of (mn)?
(1) m^n = 1/81
(2) n^m =-(1/64)

i doubt for B...Oa is B..

pl explain your choice.

It should be B.

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Fri Jan 21, 2011 10:35 am

yeah it should be C...!!!
thanks guys.

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