anupam87 wrote:
Hi
Bunuel chetan2u,
is there a quicker way to solve this problem. It took almost 2 minutes for me to get through all the answer choices. Since this is an easier problem, it would be nice if there is a better way to approach this question to save some time on the exam.
Thanks!
Hi,
There are few perfect numbers, so the best way to know these 6,28,496, 8128, but you are not required to worry much on these. If it comes on GMAT, it will be limited to factorising and finding answers, that is the choices will be small enough for you to work upon.
Just for your knowledge, the other properties related to perfect numbers is
It is of type \((2^n-1)(2^{n-1})\), so you can separate out 2s and check for the power.
For example 28=4*7=2^2*7=2^(3-1)*7, so n=3 and 2^3-1=7 is prime.
Also the perfect numbers are equal to sum of first n positive integers.
Example 6=1+2+3 and 28=1+2+...+7
Note- all perfect numbers are sum of first n natural numbers but vice versa may not be true.
So don’t worry on higher values in the choices. The question is just to test your ability to grasp on number properties or functions.
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