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Is a negative?

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Math Expert
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Is a negative?  [#permalink]

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New post 06 Dec 2016, 00:29
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

80% (00:58) correct 20% (00:59) wrong based on 54 sessions

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Re: Is a negative?  [#permalink]

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New post 06 Dec 2016, 02:53
1
Bunuel wrote:
Is a negative?

(1) (1 + a)^3 is negative.
(2) 1 – a is positive.


from 1

1+a < 0

i.e. 1<-a thus a<-1 , a is negative ... suff

from 2

1-a >0 1>a ( a could be +ve fraction 0 or negative ... insuff

A
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Re: Is a negative?  [#permalink]

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New post 12 Dec 2016, 08:08
Bunuel wrote:
Is a negative?

(1) (1 + a)^3 is negative.
(2) 1 – a is positive.


Given

Stat 1: (1 + a)^3 is negative

We can take it as (1 + a)^3 = -ve and when we are getting -ve result with cube power then 1+a = - ve => a = -ve - 1 .... a = - ve ... Sufficient.

Stat 2: 1-a = +ve => 1 - ve = a...now we can plug values...when -ve is 1 then we get a as 0....when a as 2,3... we get a as some -ve result...There are two sufficient cases possible to eliminate this option.

Option A is correct.
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Re: Is a negative?  [#permalink]

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New post 09 Apr 2019, 18:36
Is A negative?

(1) (1 + a)^3 is negative.
(2) 1 – a is positive.

A is not shown to be an integer.
Statement 1:
if a = -0.1, (1 + a)^3 will not be negative
if a = -1.1, (1 + a)^3 will be negative
so, isn't statement 1 insufficient?

Statement 2:
if a = -0.1, (1 - a) will be positive
if a = 0.9, (1 - a) will be positive
so, isn't statement 2 insufficient?

Combining both of them,
(1 + a)^3 will be negative and (1-a) to be positive

if a = -0.1, (1 + a)^3 will not be negative and (1-a) will be a positive.... This also doesn't satisfy the condition
Hence, shouldn't the answer be E?
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Re: Is a negative?  [#permalink]

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New post 09 Apr 2019, 19:34
IMO A

statment 1

(1+a)^3 is negative is only possible when a is negative

becase (x)^odd number is negative only when x is negative

here 1+a can be negative only when a is negative

sufficient


statement 2
for 0<a<1

and it is valid for a<0, and for 0<a<1 also

so a can be positive and negative both

insufficient


IMOA

award kudos if helpful

Posted from my mobile device
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Re: Is a negative?  [#permalink]

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New post 09 Apr 2019, 21:06
m1033512 wrote:
IMO A

statment 1

(1+a)^3 is negative is only possible when a is negative

becase (x)^odd number is negative only when x is negative

here 1+a can be negative only when a is negative

sufficient


statement 2
for 0<a<1

and it is valid for a<0, and for 0<a<1 also

so a can be positive and negative both

insufficient


IMOA

award kudos if helpful

Posted from my mobile device


Statement 1:
here 1+a can be negative only when a is negative: this need not be necessarily true. if -1<a<0, then inspite of a being engative, (1+a)^3 is positive
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Re: Is a negative?   [#permalink] 09 Apr 2019, 21:06
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