If m m and n n are positive integers, is the remainder of

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m and n are positive integer. Is the remainder of [(10^m)+n]/3 greater than the remainder of [(10^n)+m]/3?

(1) m>n

(2) The remainder of n/3 is 2

OA=B

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by Jay@ManhattanReview » Sun Apr 30, 2017 11:21 pm
ziyuenlau wrote:m and n are positive integer. Is the remainder of [(10^m)+n]/3 greater than the remainder of [(10^n)+m]/3?

(1) m>n

(2) The remainder of n/3 is 2

OA=B
The remainder of (10^p)/3 is always 1, irrespective of the values of p; where p is a positive integer.

Thus the rephrased question is: Is the remainder of [1 + n]/3 greater than the remainder of [1 + m]/3?

Statement 1: m > n

Case 1: m = 3 and n = 2

The remainder of [1 + n]/3 = [1 + 2]/3 = 0

The remainder of [1 + m]/3 = [1 + 3]/3 = 1.

0 < 1. The answer is No.

Case 2: m = 5 and n = 3

The remainder of [1 + n]/3 = [1 + 3]/3 = 1

The remainder of [1 + m]/3 = [1 + 5]/3 = 0.

1 > 0. The answer is Yes. No unique answer. Insufficient.

Statement 2: The remainder of n/3 is 2

Say n = 3x + 2

Thus, the remainder of [1 + m]/3 = [1 + 3x + 2]/3 = [3x + 3] / 3 = 3(x+1)/3 = 0; since the numerator 3(x+1) is a factor of 3.

Since any number divisible by 3 can have 0, 1, or 2 as its remainder, and the remainder of [1 + n]/3 = 0, the remainder of [1 + m]/3 CANNOT be less than 0.

Or, in other words, the remainder of [(10^m)+n]/3 is NOT greater than the remainder of [(10^n)+m]/3. Sufficient.

The correct answer: B

Hope this helps!

Relevant book: Manhattan Review GMAT Data Sufficiency Guide

-Jay
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by GMATGuruNY » Mon May 01, 2017 2:22 am
If m and n are positive integers, is the remainder of (10^m + n)/3 larger than the remainder of (10^n + m)/3 ?

1. m > n
2. The remainder of n/3 is 2
When a POWER OF 10 is divided by 3, the remainder will always be 1.
10/3 = 3 R1.
100/3 = 33 R1.
1000/3 = 333 R1.

From there, the remainders will proceed in the following CYCLE: 2, 0, 1...2, 0, 1...2, 0, 1...
To illustrate:
(10 + 1)/3 = 11/3 = 3 R2.
(10 + 2)/3 = 12/3 = 4 R0
(10 + 3)/3 = 13/3 = 4 R1.

(10 + 4)/3 = 14/3 = 4 R2.
(10 + 5)/3 = 15/3 = 5 R0.
(10 + 6)/3 = 16/3 = 5 R1.

(100 + 1)/3 = 101/3 = 33 R2.
(100 + 2)/3 = 102/3 = 34 R0
(100 + 3)/3 = 103/3 = 34 R1.

(100 + 4)/3 = 104/3 = 34 R2.
(100 + 5)/3 = 105/3 = 35 R0.
(100 + 6)/3 = 106/3 = 35 R1.

Notice that the cycle of remainders is the SAME whether integer values are added to 10 or to 100.
Thus, the question stem can be rephrased in terms of 10:
Is the remainder of (10 + n)/3 larger than the remainder of (10 + m)/3?

Statement 1: m>n
Case 1: m=5 and n=2
(10 + n)/3 = 12/3 = 4 R0.
(10 + m)/3 = 15/3 = 5 R0.
Here, the remainders are EQUAL, so the answer to the question stem is NO,

Case 2: m=5 and n=1
(10 + n)/3 = 11/3 = 3 R2.
(10 + m)/3 = 15/3 = 5 R0.
Here, the first remainder of (10 + n)/3 is GREATER, so the answer to the question stem is YES.
INSUFFICIENT.

Statement 2: The remainder of n/3 is 2
Options for n are 5, 8, 11, 14...
If n=5, then (10 + n)/3 = 15/3 = 5 R0.
If n=8, then (10 + n)/3 = 18/3 = 6 R0.
If n=11, then (10 + 11)/3 = 21/3 = 7 R0.
The examples above illustrate that -- in every case -- the remainder of (10 + n)/3 will be 0.
Thus, the answer to the question stem is NO:
Since the remainder of (10 + n)/3 is 0, it is not possible that the remainder of (10 + n)/3 is larger than the remainder of (10 + m)/3.
SUFFICIENT.

The correct answer is B.
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