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by ruplun » Fri Jul 15, 2011 7:17 am
If n is a positive integer and r is the remainder when 4 + 7n is divided by 3, what is the value of r?

a. n+1 is divisible by 3
b. n>20
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by vineeshp » Fri Jul 15, 2011 7:37 am
OA is A?

1) n + 1 is divisible by 3 = 3,6,9 etc. n is 2,5,8 etc

n=2 --> 4 + 7n = 4 + 7*2 = 18 . now as n increases the numbers keep adding 21 to itself ( for eg. n =5 --> 4 + 7n =39 etc.... ) So it always leaves the same remainder (0 in this case.)

2) n > 20. for different ns we can get diff values and remainders. hence not sufficient.
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by krishnasty » Fri Jul 15, 2011 7:42 am
IMO A ,

1. n+1 is divisible by 3...
by this, n can be 2,5,8 and so on....
plug in the number in the equation, the remainder always come out to be 0
Sufficient

2. n > 20
take n = 21. check remainder..not zero
take n =23, remainder = 0
hence, not sufficient.
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by Anurag@Gurome » Fri Jul 15, 2011 10:01 am
ruplun wrote:If n is a positive integer and r is the remainder when 4 + 7n is divided by 3, what is the value of r?

a. n+1 is divisible by 3
b. n > 20
Statement 1: (n + 1) is divisible by 3.
So, 7(n + 1) is also divisible by 3.
--> (7n + 7) is also divisible by 3.
--> (7n + 4 + 3) is also divisible by 3.
--> (7n + 4) is also divisible by 3.

Hence, r = 0

Sufficient

Statement 2: n > 20
r can have different values for different values of n.

Not sufficient

The correct answer is A.
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