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NDA 1 2024 Maths, question 17

Topic: Algebra

Q17

Four digit numbers are formed by using the digits 1,2,3,51,2,3,5 without repetition of digits. How many of them are divisible by 44 ?

  1. (a) 120120
  2. (b) 2424
  3. (c) 1212
  4. (d) 66Correct answer

Solution.

Answer: (d) 66

  1. Divisibility by 4 depends on the last two digits.
  2. The available endings are 12, 32 and 52.
  3. For each ending, the two remaining distinct digits can be ordered in 2! ways.
  4. Thus there are 3×2=6 numbers.