Civil Services Prep

Prelims 2022 · CSAT / Quantitative Aptitude · Question 66

Let p be a two-digit number and q be the number consisting of same digits written in reverse order. If p x q = 2430, then what is the difference between p and q?

  1. 45
  2. 27
  3. 18
  4. 9

Answer

9

Re-checking: let p = 10a + b and q = 10b + a. Then p × q = 2430. The valid reversed two-digit factor pair is 54 and 45, and 54 × 45 = 2430. So the difference is 54 - 45 = 9.

  • (a) 45: Actual difference is not 45. Incorrect.
  • (b) 27: Actual difference is not 27. Incorrect.
  • (c) 18: Actual difference is not 18. Incorrect.
  • (d) 9: 54 - 45 = 9. Correct.

My earlier conclusion of (b) was a mistake; the correct answer is (d).

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