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CTET 8 Feb 2026 Paper 1, Question 57

Topic: Numbers

Q57

If HCF of two numbers is 18, then which of the following cannot be their LCM ?

  1. (1) 128Correct answer
  2. (2) 108
  3. (3) 72
  4. (4) 144

Solution.

CBSE answer: (1)

Answer: (1) 128

  1. The HCF always divides the LCM, so the LCM must be a multiple of 18.
  2. 108=18×6108 = 18 \times 6, 72=18×472 = 18 \times 4, 144=18×8144 = 18 \times 8: all multiples of 18.
  3. 128=27128 = 2^7 has no factor 3, so 18 does not divide it.
  4. Hence 128 cannot be the LCM.