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Let's consider \(10^M\)

at M>=0: \(10^M = {1, 10, 100, 1000....}\) or \(3k+1\)
at M<0: 10^M is a fraction and our expression is not an integer.

Now, let's see our statements:

1) N=5
at M>=0: (3k+1 + 5) /3 = k+2 - an integer
at M<0: a fraction.
insufficient

2) MN is even
a) at M=2, N=5 our expression is an integer
b) at M=-2, N=-5 our expression in a fraction
insufficient

1)&2) N=5 & MN is even --> N=5, M is even
For all even M>=0 we will get an integer.
Now we have interesting question: Could negative numbers be even or odd?
if yes, we can choose M=-2, N=5 and get a fraction.
if no, M cannot be negative and two statements are sufficient.

Judging by https://en.wikipedia.org/wiki/Even_and_odd_numbers negative integers can be classified as odd/even. So, our answer is insufficient.

E
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how did you get 3k + 1? can someone please explain? thanks.
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10^K = 3k+1: for any K>=0
It means any number which is 10^K i.e. 1,10,100,1000 ..., when divide by 3, gives remainder 1.
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Thanks I committed 2 careless mistakes

Initially I chose A ignoring the fact M and are just integers not positive integers

and then I chose C since MN is even I just assumed it is positive.

but the correct ans is E since both statements would be insufficient to ans the question
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If M and N are integers, is ((10^M)) + N)/3 an integer?

(1) N = 5
(2) MN is even

Answer to question is .

From statement 1 and 2, M has to be Even Positive as N = 5 and MN is even.

Now when 5 is added to 10^M where M is even positive and then divided by 3 it always results into an integer.

M25-07
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Thanks for the question...I missed the negative case in this question as well.

Bunuel, thanks for solving.
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Hi,

"I read in a forum that negative numbers cannot be tagged as odd or even. So, if I get a DS question stating that X is a even integer, then it also implies that X>=0."

However, in the question given below, the logic is not holding true. I was considering the right answer to be C), because if MN = even and N =5 , then it implies that M must be odd integer (and hence M is > 0). Can you clarify if the argument above is false?

If M and N are integers, is 10M+N3 an integer?
(1) N=5

(2) MN is even

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.EACH statement ALONE is sufficient.Statements (1) and (2) TOGETHER are NOT sufficient.Mark as a guessHide Answer
The question does not mention whether M and N are positive. Hence, the statements taken together are not sufficient because the answer is YES if M=2, N=5 and NO if M=−2; N=5.


The correct answer is E
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Hi,

"I read in a forum that negative numbers cannot be tagged as odd or even. So, if I get a DS question stating that X is a even integer, then it also implies that X>=0."

However, in the question given below, the logic is not holding true. I was considering the right answer to be C), because if MN = even and N =5 , then it implies that M must be odd integer (and hence M is > 0). Can you clarify if the argument above is false?

If M and N are integers, is 10M+N3 an integer?
(1) N=5
(2) MN is even


First, every number except zero "0" can be categorized either Even or odd.
Secondly, "X is a even integer" does not necessarily mean X>=0. X can be smaller than 0 as well.
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SurabhiStar
Hi,

"I read in a forum that negative numbers cannot be tagged as odd or even. So, if I get a DS question stating that X is a even integer, then it also implies that X>=0."

However, in the question given below, the logic is not holding true. I was considering the right answer to be C), because if MN = even and N =5 , then it implies that M must be odd integer (and hence M is > 0). Can you clarify if the argument above is false?

If M and N are integers, is 10M+N3 an integer?
(1) N=5
(2) MN is even


First, every number except zero "0" can be categorized either Even or odd.
Secondly, "X is a even integer" does not necessarily mean X>=0. X can be smaller than 0 as well.

1. EVEN/ODD

An even number is an integer that is "evenly divisible" by 2, i.e., divisible by 2 without a remainder.

An odd number is an integer that is not evenly divisible by 2.

According to the above both negative and positive integers can be even or odd.

2. ZERO

Zero is an even integer. Zero is nether positive nor negative, but zero is definitely an even number.

An even number is an integer that is "evenly divisible" by 2, i.e., divisible by 2 without a remainder and as zero is evenly divisible by 2 then it must be even (in fact zero is divisible by every integer except zero itself).

Hope it helps.
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Hi All,

This DS question can be solved by TESTing VALUES, but you have to thorough with your TESTs and thinking.

We're told that M and N are INTEGERS. We're asked if (10^M + N)/3 is an integer. This is a YES/NO question.

Fact 1: N = 5

IF....
M = 0
N = 5
6/3 IS an integer and the answer to the question is YES.

IF...
M = 1
N = 5
15/3 IS an integer and the answer to the question is YES.

At this point, it might be tempting to say that Fact 1 is sufficient, but we have NOT yet considered ALL TYPES of integers....

IF...
M = -1
N = 5
5.1/3 is NOT an integer and the answer to the question is NO.
Fact 1 is INSUFFICIENT

Fact 2: MN is EVEN

IF...
M = 0
N = 5
6/3 is an integer and the answer to the question is YES.

IF....
M = 0
N = 1
2/3 is NOT an integer and the answer to the question is NO.
Fact 2 is INSUFFICIENT

Combined, we know....
N = 5,
MN is EVEN

IF....
M = 0
N = 5
6/3 is an integer and the answer to the question is YES.

IF....
M = -2
N = 5
5.01/3 is NOT an integer and the answer to the question is NO.
Combined, INSUFFICIENT

Final Answer:
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Nice question....

Initially didnt observe that M can be negative....then it looked too easy....well had it come in the early part of real test....i wud have thought im still in easy qtns zone....and put it as A

Thanks for posting the question
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If M and N are integers, is ((10^M)) + N)/3 an integer?

(1) N = 5
(2) MN is even

Answer to question is .

From statement 1 and 2, M has to be Even Positive as N = 5 and MN is even.

Now when 5 is added to 10^M where M is even positive and then divided by 3 it always results into an integer.

M25-07

Question: Is ((10^M)) + N)/3 an integer?
Re-worded: Is (10^M + N) a multiple of 3?

Note that 10^M will be something like 1000... if M is non-negative. Then, 10^M will be of the form (3a+1) because it will leave remainder 1 when divided by 3. If M is negative, 10^M will not be an integer.

Assuming M is non-negative, for 10^M + N to be a multiple of 3, N should be of them form 3n+2.

(1) N = 5
We don't know whether M is non-negative. Not sufficient.

(2) MN is even
again, we don't know whether M is non-negative. Not sufficient.

Using both, we know that M is even since N = 5 (odd) but we don't know whether it is non-negative.

Answer (E)
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chiragatara
If M and N are integers, is ((10^M)) + N)/3 an integer?

(1) N = 5
(2) MN is even

Answer to question is .

From statement 1 and 2, M has to be Even Positive as N = 5 and MN is even.

Now when 5 is added to 10^M where M is even positive and then divided by 3 it always results into an integer.

M25-07

Question: Is ((10^M)) + N)/3 an integer?
Re-worded: Is (10^M + N) a multiple of 3?

Note that 10^M will be something like 1000... if M is non-negative. Then, 10^M will be of the form (3a+1) because it will leave remainder 1 when divided by 3. If M is negative, 10^M will not be an integer.

Assuming M is non-negative, for 10^M + N to be a multiple of 3, N should be of them form 3n+2.

(1) N = 5
We don't know whether M is non-negative. Not sufficient.

(2) MN is even
again, we don't know whether M is non-negative. Not sufficient.

Using both, we know that M is even since N = 5 (odd) but we don't know whether it is non-negative.

Answer (E)

should the answer not be A as statement one tells us that the expression will be an integer. the question asks if the expression will be an integer and it is clearly visible that the statement 1 with N=5 will not leave a remainder and hence be divisible and hence will be an integer. Is this not sufficient to answer. the expression can also be written as (10^m)/3 + (N/3) = (1^m)/3 + 5/3= remainder of 0 and hence will be an integer. theoretically this should suffice, however, plugging values is a different result. please clear the doubt.
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Hi kaulshanx,

The prompt tells us that M and N are integers. It does NOT state that they are necessarily positive integers though. If you assume that M and N are positive, then your deduction is correct. However, what if M = -1.....? That IS an integer, but it will NOT lead to an integer result when you answer the question.

GMAT assassins aren't born, they're made,
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I made one of the classic mistake of considering M only as a positive integer when i read M and N are integers and chose option A incorrectly.

Good question
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statement 1:
10^1+5/3=Integer
10^-1+5=(1/10+5)/3=Not an integer
INSUFFICENT

Statement 2:
Clearly insufficent

1&2, clearly insufficent

Hence---> E.
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I thought I had this one in the bag lads! I selected A.... which is not the correct answer. lots of people fail in this trap, including myself.

lesson learned here is to use ALL information available in the stem AND infer correctly.

Given - M and N are integers
inference (M and N could be -int,0,inf).

test points should include negative numbers as well as positive ones!

Cheers!
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