Tough math problems + permutations/combinations

[ssang]

I'm posting tough math problems that I've received from Kirtanasarin on Test Magic
https://www.urch.com/forums/just-finishe ... notes.html

I've basically reclassified and split them up to 2 different word doc. Also added a few of my own problems.

Note there are two documents here:
1. gmat more difficult questions
2. permutations & combinations

[richardwang6430]

Do you have answer with explanation?

[gabriel]

ssang, thank you for sharing this. But are you sure there is no copyright issues with these questions.

[gabriel]

Do you have answer with explanation?

Hey richard, just post the questions you have trouble with on the forum. I am sure you will get the required explanations and answers

[mbadreams]

1. 2n is an integer
2. 3n is an integer

Data sufficiency qstn in the attached document. Answer given is D. Can some one explain how?

This is my answer.

1. Insufficient.

if n = 1/2 2n is integer. but n is not integer
if n= 2 , 2n is integer and n is integer.

2. Insufficient

if n = 1/3 3n is integer. but n is not integer
if n= 3 , 3n is integer and n is integer.

Both together if 2n is integer and 3n is integer,
then n is inetger . Sufficient.
IMO C[/spoiler]