UPSC Prelims 2019·CSAT·Quantitative Aptitude·Algebra

If x is greater than or equal to 25 and y is less than or equal to 40, then which one of the following is always correct?

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  1. Ax is greater than y
  2. B(y - x) is greater than 15
  3. C(y - x) is less than or equal to 15Correct
  4. D(x - y) is greater than or equal to 65

Explanation

The given conditions are: 1. x is greater than or equal to 25 (x >= 25) 2. y is less than or equal to 40 (y = 25 which implies -x <= -25 (multiplying an inequality by -1 reverses the sign) Adding these two inequalities: y + (-x) <= 40 + (-25) y - x <= 15 This inequality is derived directly from the given conditions and is always true. Hence, this option is always correct. D) (x - y) is greater than or equal to 65 To find the minimum possible value of (x - y), we take the minimum possible x and the maximum possible y. Minimum x = 25 Maximum y = 40 So, the minimum value of (x - y) = 25 - 40 = -15. Since (x - y) can be -15, it is not always greater than or equal to 65. Hence, this is not always correct. Therefore, the only statement that is always correct is C.
Quantitative Aptitude: If x is greater than or equal to 25 and y is less than or equal to 40, then which one of the following is always correct

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