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I'm guessing you mean: f(x) = 2^x * 3^y * 5^z. Otherwise there is not a unique answer here. If f(m) = 9f(v) = 3^2 f(v), then the exponent on the 3 must be two greater in f(m) than in f(v) while the other exponents must be the same, which means the tens digit is two greater in m than in v, so the two numbers must differ by 20.vaivish wrote:The function f is defined for each positive three-digit integer n by f(n) = 2x3y5z , where x, y and z are the hundreds, tens, and units digits of n, respectively. If m and v are three-digit positive integers such that f(m)=9f(v), them m-v=?
(A)8
(B)9
(C)18
(D)20
(E)80
That's all correct, but notice that if we accept the question as written, and v = 111, then m could be 119, 191, 911, 331, 313 or 133. If m is 191, then m-v would be 80, not 8. That's why I was quite sure that the question was not typed correctly- there would be more than one correct answer if it were. I'd also expect to see "2x3y5z" written differently- it's just equal to 30xyz (and the 30 is irrelevant to the question).oldgeezer wrote:I think it is A, 8. IF you meant it like written, 2x3y5z, then the lowest possible number is 111 (any zeros would make the function 0 and therefore nothing could be 9 times its value)
the function of 111 is 30
I chose this number to start because the values of the answers are not that large and making the numbers much bigger quickly eliminates all answers
Anyway, since the value of the function of the other number must be 9 times 30 or 270, I came up with the number 119, since the value of its function is 270 (2*3*45) and the difference with 111 is 8.
I don't think there are any other combinations of numbers that satisfy the 9x function value and any of the answers
OF COURSE, this took more than 2 minutes!!! and this is what kills me about this test
old geezer
Well, I'm not sure where the question in the above post is from, but yes, you might be surprised by how much thought goes into writing the wrong answer choices for real GMAT questions. If you analyze the answer choices to almost any appropriate GMAT question, you can normally work out why most of them are there- that is, work out what common mistake the question designer has anticipated. Just choosing a random example from the OG (qn 126), and simplifying the language to save me some typing (:)):oldgeezer wrote: I am actually shocked there is another combination BY CHANCE when the problem is written incorrectly... or does this show how far the GMAT people will go to find answers you might get to the wrong way? you woul dhave to missinterpret the exponents for factors... wow do they go THAT far in searching for the "right" wrong answers?
couuld u please expain with much easier examplesOtherwise there is not a unique answer here. If f(m) = 9f(v) = 3^2 f(v), then the exponent on the 3 must be two greater in f(m) than in f(v)
Hi vaivish- it's not your fault, obviously, but whoever published the question didn't print it correctly. The x, y and z are supposed to be exponents. So the question should read:vaivish wrote:hey thanks a ton...but the question posted is right.....i have checked it again...but forgot the source.....
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