Rainman91
Correct me if I am wrong. I do not see any info regarding n, would we still be able to answer the question?
Yep. Typo. Edited.
This is DEFINITELY, a hard, 700+, MAYBE EVEN 750+, question. Below is a complete, step-by-step solution.
Official Solution:If \(m\) and \(n\) are positive integers, and \(x = 2^m3^n\), is \(m < n\) ?This is certainly a challenging question, likely in the range of 700 or even 750 difficulty level. Find a detailed, step-by-step solution below.
(1) \(x\) is divisible by 144.
Factor 144:
\(144 = 2^4*3^2\).
The above means that \(m \geq 4\) and \(n \geq 2\). This is not enough to conclude whether m < n. For example:
If \(x = 2^4*3^4=1296\), then the answer is NO: \((m=4) = (n=4)\) (notice that 144 IS a factor of 1296).
If \(x = 2^4*3^5=3888\), then the answer is YES: \((m=4) < (n=5)\) (notice that 144 IS a factor of 3888).
Not sufficient.
(2) \(x\) is
not divisible by 648
Factor 648:
\(648 = 2^3*3^4\).
The above means that either \(m < 3\) OR \(n < 4\) (to put it simply, for x
not to be divisible by \(648 = 2^3*3^4\), EITHER the power of 2, which is \(m\), must be less than 3 OR the factor of 3, which is \(n\), must be less than 4 (or both)). This is not enough to conclude whether \(m < n\). For example:
If \(x = 2*3=6\), then the answer is NO: \((m=1) = (n=1)\) (notice that 6 is NOT divisible by 648).
If \(x = 2*3^2=18\), then the answer is YES: \((m=1) < (n=2)\) (notice that 18 is NOT divisible by 648).
Not sufficient.
(1)+(2) When combining, we get that \(m\) cannot be less than 3 (from (2)), because from (1) we know that \(m \geq 4\), thus
\(m \geq 4\) must be true (from (1)). Now, since \(m \geq 4\), then from (2)
\(n < 4\) must be true. Therefore, \(m > n\) and we get a definite NO answer to the question.
Sufficient.
Answer: C