Here is how I approached this problem and most GMAT problems.Simplify the prompt as much as you can.
We know n is an integer and (4+7n)/3 will give a remainder r.
Lets assume n=1 11/3. Rem =2
n=2 18/3 rem=0
n=3 25/3 rem =1
n=4 32/3 rem =2
n=5 39/3 rem =0
You can see a pattern : 2,0,1,2,0,1,2... So if we know n we can find what the remainder is.
When the term is 2nd,5th,8th,11th the rem =0
When the term is 1st,4th,7th,10th the rem =2
When the term is 3rd,6th,9th the rem =1
1) n+1 divisible by 3. if n =2 .n+1 is divisible by 3. Rem @ n=2 is 0.
When n+1=6 or n =5 rem 0
n+1=9 n-> 8 rem = 0
In general you can say n->2,5,8,11,14.See it matches with value 0
Sufficient.
2) This is clearly insufficient as n could be 21,or 22,or 23 or anything.
For 21. rem =1
For 22 rem =2.
Multiple values.hence insufficient.
Answer should be A
