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a < 0 < b

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a < 0 < b [#permalink] New post 15 Feb 2017, 08:46
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Question Stats:

76% (00:36) correct 23% (00:44) wrong based on 72 sessions


\(a < 0 < b\)

Quantity A
Quantity B
\(a^{-10}\)
\(b^{-5}\)


A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

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Re: a < 0 < b [#permalink] New post 21 Feb 2017, 16:32
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Explanation

The best strategy to solve these problems is by plugging values

Put a = -1 and b = 1, then we have

Quantity A is \(-1^{10} = 1\)

Quantity B is \(1^5 =1\)

Clearly, the quantities are equal. Now put a = -2 and b = 1

Quantity A is \(-2^{10} = 1024\)

Quantity B is \(1^5 =1\)

Now Quantity A is greater. Clearly, both A and C cannot be right at the same time so option D is the correct choice!
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Re: a < 0 < b [#permalink] New post 10 Aug 2017, 08:35
But the question states a^-10 power and b^-5... and a < 0 < b

-1^-10 = -1
1^-5 = 1

In what circumstance can A and B be equal if you raise them to a negative power?

Ok, I am an idiot - I was playing with the equation in my calculator, which is why it was driving me nuts... because I was almost positive it was wrong... I was inputting -1^-10, and not (-1)^-10... You are correct.
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Re: a < 0 < b [#permalink] New post 19 May 2018, 09:38
I think the entity A will be a faction with a negative sign and entity B will be postive ..becasue the entity A is negative in nature ?

Please elaborate.
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Re: a < 0 < b [#permalink] New post 19 May 2018, 16:36
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IshanGre wrote:
I think the entity A will be a faction with a negative sign and entity B will be postive ..becasue the entity A is negative in nature ?

Please elaborate.


\(a\) is a negative number may or maynot be a fraction. However it is raised to even power.
If \(a\) is a fraction then \(a^{-10}\) is a number greater than 1.
if \(|a| > 1\) then \(a^{-10}\) is a fraction.

However in both cases they are positive.
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Re: a < 0 < b [#permalink] New post 21 May 2018, 06:13
sandy wrote:
IshanGre wrote:
I think the entity A will be a faction with a negative sign and entity B will be postive ..becasue the entity A is negative in nature ?

Please elaborate.


\(a\) is a negative number may or maynot be a fraction. However it is raised to even power.
If \(a\) is a fraction then \(a^{-10}\) is a number greater than 1.
if \(|a| > 1\) then \(a^{-10}\) is a fraction.

However in both cases they are positive.



I can see but the question stem says that the a is raised to the power of negative 10? pls elaborate
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Re: a < 0 < b [#permalink] New post 21 May 2018, 12:19
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Say a=\(\frac{-1}{2}\) then \(a^{-10}=(\frac{-1}{2})^{-10}= 2^{10}\).

Also a=\(-2\) then \(a^{-10}=(-2)^{-10}= (\frac{-1}{2})^{10}=\frac{1}{2^{10}}\).

I hope this was this was your issue.
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Re: a < 0 < b [#permalink] New post 16 Jul 2018, 17:53
How is it not B?

When we set a = -1 and b = 1:
qty1) -1^-10) = -1/1^10 = -1
qty2) 1^5 = 1

Thus QTY 2 is bigger.

Lets make a=-2 and b=2:
qty1) -2^-10 = -1/2^10
qty2) 2^5 = 32

Clearly a negative fraction is smaller than 32 making qty 2 greater again.

This has to mean that B is the answer. Why would it be D?
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Re: a < 0 < b [#permalink] New post 17 Jul 2018, 13:29
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Your calculations are wrong.

\(a^{-10} = \frac{1}{a^{10}}\) and if \(a\) is \(-1 = 1^{10} = 1\). So a ends up being positive.
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Re: a < 0 < b   [#permalink] 17 Jul 2018, 13:29
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