Reasoning : Logical Reasoning & Analytical Ability

Q 44 / 325

UPSC CSE Prelims 2024

A Question is given followed by two Statements I and II. Consider the Question and the Statements.

Question: Is (x + y) an integer?

  1. Statement-I: (2x+y) is an integer.
  2. Statement-II: (x+2y) is an integer.

Which one of the following is correct in respect of the above Question and the Statements?

EXPLANATION

Correct Option

The Question asks whether (x + y) is an integer.

Statement-I: (2x + y) is an integer.

Consider an example: If 2x + y = 3. If x = 1, then y = 1, making x + y = 2 (an integer). However, if x = 1.5, then y = 0, making x + y = 1.5 (not an integer). Therefore, Statement-I alone is insufficient to determine if (x + y) is an integer.

Statement-II: (x + 2y) is an integer.

Consider an example: If x + 2y = 3. If y = 1, then x = 1, making x + y = 2 (an integer). However, if y = 1.5, then x = 0, making x + y = 1.5 (not an integer). Therefore, Statement-II alone is insufficient to determine if (x + y) is an integer.

Combining Statement-I and Statement-II:

  • From Statement-I, (2x + y) is an integer.
  • From Statement-II, (x + 2y) is an integer.

Adding these two expressions: (2x + y) + (x + 2y) = 3x + 3y = 3(x + y).

Since the sum of two integers is an integer, 3(x + y) must be an integer. Let 3(x + y) = K, where K is an integer. This implies x+y=K3.

The expression K3 may or may not be an integer. For instance, if K = 3, then x + y = 1 (an integer). If K = 4, then x+y=43 (not an integer).

Thus, even by using both statements together, it cannot be definitively determined whether (x + y) is an integer.

Incorrect Options

Options 1, 2, and 3 are incorrect because, as demonstrated above, neither statement alone nor both statements combined are sufficient to answer the question.