Sarkari RiseLogin
UPSC CSE 2025 · PYQ · Number System / LCM and HCF · hard

There are n sets of numbers each containing only three positive integers whose LCM is equal to 1001 and HCF is equal to 1. What is the value of n ?

  1. A.6
  2. B.7
  3. C.8
  4. D.More than 8✓ Correct

Explanation

1001 = 7 × 11 × 13. We need ordered/unordered triples of positive integers with LCM = 1001 and HCF = 1. The divisors of 1001 are {1, 7, 11, 13, 77, 91, 143, 1001} — 8 divisors. We need to choose three divisors such that their LCM is 1001 and HCF is 1. Considering unordered triples: many combinations like (1, 7, 1001), (1, 11, 1001), (1, 13, 1001), (7, 11, 13), (7, 11, 143), (7, 13, 77), (11, 13, 91), (1, 77, 13), (1, 91, 11), (1, 143, 7), etc. Counting carefully yields more than 8 such triples. Hence the answer is 'More than 8'.
💡 Practice unlimited UPSC CSE PYQs + AI-tracked progress on each topic. Sign up free →

More Number System / LCM and HCF questions

Want more UPSC CSE practice?

Free daily 10-Q quiz · adaptive mocks · 4,000+ verified PYQs · AI doubt solver in Hindi + English

Sign up freeMore Number System / LCM and HCF practice