GMAT 700 Level Arithmetic Practice Question 36

Number Properties | Positive Integers | Data Sufficiency Practice

The given question is a GMAT Hard Math data sufficiency question. This question is a GMAT arithmetic practice question that tests your understanding of properties of positive integers from the topic Number Properties.

This data sufficiency problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in a leap year or the meaning of the word counterclockwise), you must indicate whether -

  1. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
  2. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
  3. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
  4. EACH statement ALONE is sufficient to answer the question asked.
  5. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
Numbers

All numbers used are real numbers.

Figures

A figure accompanying a data sufficiency question will conform to the information given in the question but will not necessarily conform to the additional information given in statements (1) and (2)

Lines shown as straight can be assumed to be straight and lines that appear jagged can also be assumed to be straight

You may assume that the positions of points, angles, regions, etc. exist in the order shown and that angle measures are greater than zero.

All figures lie in a plane unless otherwise indicated.

Note

In data sufficiency problems that ask for the value of a quantity, the data given in the statement are sufficient only when it is possible to determine exactly one numerical value for the quantity.

Question 36: What is the value of (m + n) if m and n are positive integers?

Statement 1: m2 – n2 = 105
Statement 2: Neither m nor n is divisible by 8.


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Explanatory Answer | GMAT Arithmetic DS Q36

Step 1: Evaluate Statement 1 ALONE

Statement 1: m2 – n2 = 105
m and n are positive integers.
m2 – n2 can be written as (m – n)(m + n). Therefore, (m – n)(m + n) = 105
Both (m – n) and (m + n) have to be positive integers. (Why? Because (m + n) is positive and the product of (m + n) and (m - n) is positive.)
The ways of expressing 105 as a product of 2 positive integers is listed in the table given below.

(m - n) (m + n)
1 105
3 35
5 21
7 15

So, (m + n) could be 105, 35, 21, or 15.
We are not able to answer the question with a UNIQUE value.
Hence, statement 1 alone is not sufficient.
Eliminate answer options A and D.


Step 2: Evaluate Statement 2 ALONE

Statement 2: Neither m nor n is divisible by 8.
Infinite possibilities exist for this condition.

We are not able to answer the question with a UNIQUE value.
Hence, statement 2 alone is not sufficient.
Eliminate answer option B.


Step 3: Evaluate Statements TOGETHER

Statement 1: m2 – n2 = 105
Statement 2: Neither m nor n is divisible by 8.

From statement 1: (m – n) (m + n) = 105 and both (m – n) and (m + n) are positive integers.

(m - n) (m + n) m n
1 105 53 52
3 35 19 16
5 21 13 8
7 15 11 4

From Statement 2: We can eliminate (19, 16) and (13, 8).
We still have two values for (m, n): (53, 52) and (11, 4)
Therefore, (m + n) could be 105 or 15.

Despite combining both the statements, we are not able to find a UNIQUE value for (m + n).
Statement TOGETHER are NOT sufficient.
Eliminate answer option C.

Choice E is the correct answer.

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