Does anyone get this manhattan gmat question. I tried to understand their reason but it didn't make any sense ... just wanna see if anyone has another way of doing it.
If a^2 is not equal to b^2, what is the value of
a - b
__________ ?
a^2 – b^2
(1) 3^b + 2 = 81
(2) a = 3^2b – 3
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Manhattan gmat DS question - doesn't make sense
This topic has expert replies
Here's the answer:
(1) SUFFICIENT: We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
(2) SUFFICIENT: We can set the right side of this equation equal to the right side of the equation in the question (both sides equal a). 3b – 1 = 32b – 3, which means that b – 1 = 2b – 3 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
The correct answer is D.
(1) SUFFICIENT: We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
(2) SUFFICIENT: We can set the right side of this equation equal to the right side of the equation in the question (both sides equal a). 3b – 1 = 32b – 3, which means that b – 1 = 2b – 3 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
The correct answer is D.
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schumi_gmat
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we have to find 1/(a+b). The a-b can be cancelled as a-b not equal to 0
From A) 3^(b+2) = 81, i.e. b+2=4 and b=2
We dont know value of a. Hence insuff
From B) a= 3^2b-3
one equation, 2 variables. Hence insuff
Hence ans is C.
From A) 3^(b+2) = 81, i.e. b+2=4 and b=2
We dont know value of a. Hence insuff
From B) a= 3^2b-3
one equation, 2 variables. Hence insuff
Hence ans is C.
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mygmat.2009
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I agree with schumi_gmat , unless sky123 is missing to give us part of the question!
Sky123, in your answer you mention equation [a = 3b – 1], yet the question you posted does not mention this equality.
Sam
Sky123, in your answer you mention equation [a = 3b – 1], yet the question you posted does not mention this equality.
Sam
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gabriel
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Where did you get a=3b-1 from?, it is not part of the question. So if the question is correct then schumi_gmat is correct.sk123 wrote:Here's the answer:
(1) SUFFICIENT: We can rewrite this equation in a base of 3: 3b + 2 = 34, which means that b + 2 = 4 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
(2) SUFFICIENT: We can set the right side of this equation equal to the right side of the equation in the question (both sides equal a). 3b – 1 = 32b – 3, which means that b – 1 = 2b – 3 and therefore b = 2.
We can plug this value into the equation a = 3b – 1 to solve for a.
The correct answer is D.
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Uri
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utterly confused! first i thought MGMAT has used technique to convert decimal number to a different base (base of 3 in stead of base of 10). but after following more carefully i understood that it was not so. don't understand from where they have got the other equation.
sk123, if you enclosed the exponents within brackets, that would have been better for understanding. but any way, this solution by MGMAT is very confusing.
if the question and the solution is reproduced correctly, then can any MGMAT tutor available here please help us?
sk123, if you enclosed the exponents within brackets, that would have been better for understanding. but any way, this solution by MGMAT is very confusing.
if the question and the solution is reproduced correctly, then can any MGMAT tutor available here please help us?
