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If bot a and b are nonzero integers, what is the value of ab

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If bot a and b are nonzero integers, what is the value of ab [#permalink] New post 15 Oct 2012, 06:40
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If bot a and b are nonzero integers, what is the value of a*b ?

(1) a^2=b^2
(2) \sqrt{b}=2

[Reveal] Spoiler:
1) a^2 - b^2 = 0 ---> (a - b) (a + b) = 0 ----> a = band a= -b insuff

2) b = 2 ---> basically \sqrt{b} = 4 or squaring both sides we have b = 4 same insuff


1) + 2)b = 4 and from one a = b-----> 4*4 =16 we havea * b suff

But the OA is different :?:
[Reveal] Spoiler: OA

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Last edited by Bunuel on 15 Oct 2012, 06:51, edited 2 times in total.
Renamed the topic and edited the question.
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Re: If bot a and b are nonzero integers, what is the value of ab [#permalink] New post 15 Oct 2012, 06:47
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The answer is E. When you sum up statements 1 and 2, you only considered the case when a=b. You forget to consider the case a=-b. This would mean that a = 4 & a = -4; the the answer cannot be determined.
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Re: If bot a and b are nonzero integers, what is the value of ab [#permalink] New post 15 Oct 2012, 06:49
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If bot a and b are nonzero integers, what is the value of a*b ?

(1) a^2=b^2 --> |a|=|b|. If a=b=1, then ab=1 but if a=b=2, then ab=4. Not sufficient.

(2) \sqrt{b}=2 --> b=4. Nothing about a. Not sufficient.

(1)+(2) Since from (2) b=4, then from (1) a^2=16, thus a=4 or a=-4 --> ab=4*4=16 or ab=(-4)*4=-16. Not sufficient.

Answer: E.

Hope it's clear.
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Kudos [?]: 2300 [0], given: 692

Re: If bot a and b are nonzero integers, what is the value of ab [#permalink] New post 15 Oct 2012, 07:08
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Bunuel wrote:
If bot a and b are nonzero integers, what is the value of a*b ?

(1) a^2=b^2 --> |a|=|b|. If a=b=1, then ab=1 but if a=b=2, then ab=4. Not sufficient.

(2) \sqrt{b}=2 --> b=4. Nothing about a. Not sufficient.

(1)+(2) Since from (2) b=4, then from (1) a^2=16, thus a=4 or a=-4 --> ab=4*4=16 or ab=(-4)*4=-16. Not sufficient.

Answer: E.

Hope it's clear.


not consider that b = 4 a= b 4*4= 16 AND a = -b 4*-4 = -16

Thanks Mod :)
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Re: If bot a and b are nonzero integers, what is the value of ab   [#permalink] 15 Oct 2012, 07:08
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