This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 484
Joined: 30 Jul 2006
Thanked: 2 times
Followed by:1 members

inequity 54

by magical cook » Sun Dec 23, 2007 11:42 am
If n denotes a numner to the left of 0 on the number line such that the square of n is less than 1/100, then the reciprocal of n must be..


1) less than -10

2) between -1 and -1/10

3) between -1/10 and 0

4) between 0 and 1/10

5) greater than 10


my way was...
n^2 , 1/100
-1/10 < n < 1/10
since n is negative
-1/10 < n
n needs to be reciprocal
-10 < n

but which is greater than -10 and which is not answer (not even an option)

Could anyone pls take a look at my procedure and give me advise where I got it wrong...

User avatar
Legendary Member
Posts: 986
Joined: 20 Dec 2006
Location: India
Thanked: 51 times
Followed by:1 members

Re: inequity 54

by gabriel » Sun Dec 23, 2007 12:34 pm
magical cook wrote:If n denotes a numner to the left of 0 on the number line such that the square of n is less than 1/100, then the reciprocal of n must be..


1) less than -10

2) between -1 and -1/10

3) between -1/10 and 0

4) between 0 and 1/10

5) greater than 10


my way was...
n^2 , 1/100
-1/10 < n < 1/10
since n is negative
-1/10 < n
Everything until here is fine
magical cook wrote: n needs to be reciprocal
-10 < n
When you take the reciprocal u need to take it on both the sides (this applies to all mathematical operations for example if you multiply one side with -2 then you have to do the same with the other side if you dont then you are changing the relation between the two sides, the same goes for addition, subtraction, division, reciprocals etc.), so the last step should have been -10<1/n.. which basically means n < -10 .. so the answer should be A ..

Master | Next Rank: 500 Posts
Posts: 484
Joined: 30 Jul 2006
Thanked: 2 times
Followed by:1 members

by magical cook » Sun Dec 23, 2007 2:08 pm
ahhh, my bad.. :oops: thank you !

Junior | Next Rank: 30 Posts
Posts: 11
Joined: 03 Dec 2007

clarification for previous explanation

by Bschool08 » Sun Dec 23, 2007 6:48 pm
magical cook, can you confirm that A is the right answer? i'm not seeing how -10<1/n is actually n<-10---i'm missing something here? if n is actually negative shouldn't taking it over to the other side yield n>10 making the answer E? if you can confirm would appreciate it - thanks

Master | Next Rank: 500 Posts
Posts: 484
Joined: 30 Jul 2006
Thanked: 2 times
Followed by:1 members

by magical cook » Sun Dec 23, 2007 7:56 pm
Hi, the answer is A (this is gmatprep question, so OA should be correct :wink: )

Junior | Next Rank: 30 Posts
Posts: 11
Joined: 03 Dec 2007

by Bschool08 » Sun Dec 23, 2007 9:21 pm
ok- thanks for confirming

Master | Next Rank: 500 Posts
Posts: 460
Joined: 25 Mar 2007
Thanked: 27 times

by samirpandeyit62 » Sun Dec 23, 2007 9:32 pm
n^2 < 1/100

i.e n <1> -1/10

since n is to the left of 0, hence n > -1/10

i.e n > -1/10

i.e 10 > -1/n

or 1/n (reciprocal of n)< -10

A
Regards
Samir