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OAU Post-UTME Mathematics 2022 (Batch A) Question 16

Question 16

Permutation and Combination

Five digit numbers are formed from digits 4, 5, 6, 7 and 8. How many of the numbers are odd, if repetitions of digits are not allowed?

  1. A.24
  2. B.12
  3. C.48
  4. D.72
Show the answer and explanation

Answer: C (48)

Explanation

An odd number must end in 5 or 7 (2 choices). The other 4 digits fill the first four places in 4! = 24 ways. 2 × 24 = 48.