UPSC Prelims 2018·CSAT·Quantitative Aptitude·Number System

X and Y are natural numbers other than 1, and Y is greater than X. Which of the following represents the largest number?

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Last updated 8 Jul 2026, 4:39 pm IST
  1. AXYCorrect
  2. BX/Y
  3. CY/X
  4. D(x + y) / xy

Explanation

Let's analyze each option based on the given conditions: X and Y are natural numbers other than 1, and Y > X. This implies X >= 2 and Y >= 3.

  1. Option B (X/Y): Since Y > X, X/Y will always be a proper fraction, meaning 0 = 2, 1/X = 3 (as Y > X and X >= 2), 1/Y X, Y/X will always be greater than 1. Example: If X=2, Y=3, then Y/X = 3/2 = 1.5.

  2. Option A (XY): This is the product of two natural numbers, both greater than or equal to 2. Since X >= 2 and Y >= 3, XY >= 2 * 3 = 6. This value will always be greater than or equal to 6. Example: If X=2, Y=3, then XY = 2 * 3 = 6.

Comparison: Options B and D are always less than 1. Option C is always greater than 1. Option A is always greater than or equal to 6.

To confirm A is the largest, we compare A and C: We need to compare XY with Y/X. Multiply both sides by X (since X is a natural number, X > 0, so the inequality direction doesn't change): XY * X vs Y/X * X X^2 * Y vs Y Divide both sides by Y (since Y is a natural number, Y > 0, so the inequality direction doesn't change): X^2 vs 1 Since X is a natural number other than 1, X must be at least 2. Therefore, X^2 >= 2^2 = 4. Since X^2 >= 4, X^2 is always greater than 1. This proves that XY is always greater than Y/X.

Therefore, XY (Option A) is the largest number.

The final answer is $\boxed{A}$

Quantitative Aptitude: X and Y are natural numbers other than 1, and Y is greater than X. Which of the following represents the largest number?

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