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Six years from now, Sumi's age will be the square of her age

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Emdad
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Six years from now, Sumi's age will be the square of her age [#permalink] Six years from now, Sumi's age will be the square of her age   06 May 2021, 08:38
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Six years from now, Sumi's age will be the square of her age six years ago. What is Sumi's age?

(A) 8
(B) 10
(C) 12
(D) 15
(E) None of these
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Re: Six years from now, Sumi's age will be the square of her age [#permalink] Six years from now, Sumi's age will be the square of her age   06 May 2021, 11:06
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Emdad wrote:
Six years from now, Sumi's age will be the square of her age six years ago. What is Sumi's age?

(A) 8
(B) 10
(C) 12
(D) 15
(E) None of these


Set Sumi's age as S, then six years from now her age would be \(S + 6.\) The square of her age six years ago would be \((S - 6)^2\).

Equating these gives \(S + 6 = S^2 - 12S + 36\)
\(S^2 - 13S + 30 = 0\)
\((S - 10)(S - 3) = 0\).

We can have \(S = 10\) or \(S = 3\) but \(S = 3\) does not make sense so we must have choice B.

Ans: B
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Six years from now, Sumi's age will be the square of her age [#permalink] Six years from now, Sumi's age will be the square of her age   06 May 2021, 11:38
Bunuel my last post was archived that's why I am posting here, the answer is E because two value is applicable for that question that is 2 and 4, but in option B there was only one value 2. So, it is not always true that answer is 2, answer is 4 also that's why the answer is E.

And I have taken this question from MBA question bank of IBA, Dhaka University.

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Re: Six years from now, Sumi's age will be the square of her age [#permalink] Six years from now, Sumi's age will be the square of her age   06 May 2021, 11:48
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Emdad wrote:
Bunuel my last post was archived that's why I am posting here, the answer is E because two value is applicable for that question that is 2 and 4, but in option B there was only one value 2 so it is not always true that answer is 2, answer is 4 also that's why the answer is E.

And I have taken this question from MBA question bank of IBA, Dhaka University.

Posted from my mobile device


Option D there says: n should be a multiple of 2. If n is an integer, then both n = 2 and n = 4 are multiples of 2 and answer is D. Next, n^2=2^n has one more solution: n = -(2 W(log(2)/2))/log(2) (n≈-0.766665) and considering this the answer is E, not because of what you've written. Anyway, not a good/proper GMAT questions. I'd suggest to stick to more reliable/good sources and not to post questions from mentioned one. Thank you.
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Re: Six years from now, Sumi's age will be the square of her age [#permalink] Six years from now, Sumi's age will be the square of her age   06 May 2021, 12:02
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Bunuel wrote:
Emdad wrote:
Bunuel my last post was archived that's why I am posting here, the answer is E because two value is applicable for that question that is 2 and 4, but in option B there was only one value 2 so it is not always true that answer is 2, answer is 4 also that's why the answer is E.

And I have taken this question from MBA question bank of IBA, Dhaka University.

Posted from my mobile device


Option D there says: n should be a multiple of 2. If n is an integer, then both n = 2 and n = 4 are multiples of 2 and answer is D. Next, n^2=2^n has one more solution: n = -(2 W(log(2)/2))/log(2) (n≈-0.766665) and considering this the answer is E, not because of what you've written. Anyway, not a good/proper GMAT questions. I'd suggest to stick to more reliable/good sources and not to post questions from mentioned one. Thank you.


Actually, as an undergraduate student, I found this forum really helpful for learning, that's why I tend to post a question that I think esoteric to me expecting that I will get the easiest and low time-consuming method to answer that question and I humbly admit that some of the questions are not standard for this forum and I will try to post a standard question next time. Thank you!
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Re: Six years from now, Sumi's age will be the square of her age [#permalink]
06 May 2021, 12:02
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