Khwarizmi
JeffTargetTestPrep
Khwarizmi
JeffTargetTestPrep gmatophobiaWhen facing this problem in the practice exam, I thought "n" could be any positive integer, not necessarily n > 3. However, that must be mistaken given how you two solve it algebraically. What threw me off is the fact that they attribute their own definition to "n*" which made me think the same was being done to "n!" instead of thinking it was a 'normal' factorial.
Do you guys perhaps have some tips about how I can avoid making such a mistake henceforth? I.e. how do I know whether they actually mean factorial or if they are attributing their own definition to a given term?
I'm not sure I understand your question. Can you rephrase it?
Also, we need not use values of n that are greater than.
The question only tells us that n is a positive integer. So, it can be 1, 2, 3, 4, 5, etc
For each positive integer n, let \(n^* = (2)(4)(6)...(2n)\) and \(n! = (1)(2)(3)...(n)\). Which of the following is equivalent to \(n^*÷n!\)?
A. (n - 1)!
B. n!
C. (n + 1)!
D. 2^n
E. 2^(n + 1)
In as simple terms as possible, I do not understand what "n" represents in this problem. To the best of my knowledge, it is supposed to represent the number of terms in the numerator or denominator respectively. I.e. since there are at least three terms [(2)(4)(6) in the numerator or (1)(2)(3) in the denominator] prior to the term containing n, then n ≥ 4. That is why I thought n must be a positive integer greater than 3.
Solving the fraction algebraically gives 16 but if n is 1 in the given answer choice (D), then the answer would be 2. That's what confuses me.
The question defines a function, denoted by *, for
each positive integer n as \(n^* = (2)(4)(6)...(2n) = 2^n * n!\). For example:
- If \(n=1\), then \(n^* = 2^n*n!=2\);
- If \(n=2\), then \(n^* = 2^n*n!=8\);
- If \(n=3\), then \(n^* = 2^n*n!=48\);
and so on.
So, if \(n = 1\), then \(n^* ÷ n! = 2:1 = 2\). Note that in the case of n = 1, both options C and D yield 2. However, the question seeks the option that is ALWAYS equivalent to \(n^* ÷ n!\), not just for specific values.
For the plug-in method, it might happen, as in the above case, that for some specific number(s), more than one option may appear to be the "correct" answer. In such cases, select some other numbers and recheck these "correct" options only. For instance, if you check for \(n = 2\), then \(n^* ÷ n! = 8:2 = 4\), and among options C and D, only option D is correct, making it the right answer.
Hope this helps.