## Saturday, August 8, 2009

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- Ariel Goldberg
- My name is Ariel Goldberg and I have been a GMAT tutor for eight years. I have taken the GMAT more than twenty times and scored into the 99th percentile; I like to share my GMAT knowledge with everybody. One of the things I like is to write GMAT quant questions that do reflect the changes in the test. The questions sold by some prep services are outdated in that they reflect the GMAT of three or four years ago, before Pearson took over. So that is where I come in, I provide people with good, real-looking GMAT questions.

Answer is A

ReplyDeletetry n=3, then r=1, i guess neither are correct.

ReplyDeleteI think answer is C (Both answer together)

ReplyDelete(1) n is even-> r might be 6 or 0

(2) n is not divisible by 5 -> n cannot be 5 0R 10; then r might be 1,6

(1)+(2) --> r = 6

trial:

1 r=1

2 r=6

3 r=1

4 r=6

5 r=5

6 r=6

7 r=1

8 r=6

9 r=1

10 r=0

n>10 repeat

Answer is (C),

ReplyDeleteIf n=even then remainder will be 6 & 0.

taking the II statement into account 0 is eliminated.

r=6 answer.

Vivek is right, statement 2 eliminates the 0 option, and so the answer is C.

ReplyDeleteIn my opinion, E.

ReplyDeleteIf, for example, n=2 or n=4, we know that both are not divisible by 5. And their remainders when n^4/10 are not the same. Thus, NS.

Hey Anonymous, sorry but you are wrong, 2^4 and 4^4 will both end in a 6, so answer is C. Sorry!

ReplyDeleteThis comment has been removed by the author.

ReplyDeleteFind n^4 (mod 10)

ReplyDelete(1) n = 0 (2), n^4 = 0 (2), but we need to know n^4 (mod 5) to get the exact figure

(2) n = 1, 2, 3, 4 (mod 5)

n^4 = 1^4, 2^4, 3^4, 4^4 = 1 (mod 5) (power up the remainders)

We need to know n^4 (mod 2) to get the exact figure.

Combing both gives: n^4 = 1 (mod 5) and n^4 = 0 (mod 2).

n^4 = 1 (mod 5) {1,6,11,16,...}

n^4 = 0 (mod 2) {0,2,4,6,8,...}

Intersection {6,16,26...}

Hence n^4 = 6 (mod 10)

Well, we don't need to get the exact remainder.

If x = p (mod a), x = q (mod b) and gcd(a,b) =1, x has a unique value modulo ab.

Typical GMAT trap

ReplyDeleteanswer C:

ReplyDeletefrom 1: n can be 2,4,6,8,10 for n=2,4,..will work but for n=10 it will not, since we do not have unique r hence not suff.

2nd, clearly not suff, as n can be 1,2, 3....

from 1 &2, n can be 2,4,6,8, or number ending with these numbers. in any case n^4 will give 6 as unit digit and hence when divided by 10, we will get unique remainder 6. suff... answer C