Gmatprep - DS - Remainder

Question

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Work appreciated.

walker · Answer

A

1. 4+7n=7n+7-3=7(n+1)-3=7*3k-3 ==> r=0 . sufficient

2. insufficient.

bsjames2 · Answer

I just did by trial and error, walker's method is probably more fool proof (though I too did not understand the logic behind it):

1) n + 1, when this is true, no matter what we plug into (4 + 7n)/3, we get R=0, thus SUFF

2) n>20 could be any integer over 20, thus INSUFF

A

pmenon · Answer

trial and error for me as well. doesnt take too much time to realize that 4+7n always gives multiples of 3, i.e. remainder is always 0.

stat 1 is enough for this

stat 2, n can be anything, and remainders will be different. insuff.

kbulse · Answer

I think walker's method is better because in some cases just picking numbers can get you wrong, for instance you tried three times and it worked, but it doesn't mean that it works with all numbers.
about substracting 3, it changes nothing 7n+4=7n+7-3 because 7-3 is 4
last point it is obvious that 7*3k-3 divided by three with remainder 0, because nothing left, it can be simplified to7k-1

jimmyjamesdonkey · Answer

Again remainders...hate them..

OA is A.

Statement 1: When true....n = 2,5,8,11...

Plug these into 7n+4/3 and we always get r=0

Statement 2: Tells us nothing.

StartupAddict · Answer

Easiest way:

4n+7 === n+1 (mod 3)

A) sufficient (duh)
B) not sufficient

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