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WAEC Further Mathematics 2008 Question 33

Question 33

Permutations and Combinations

If n items are arranged two at a time, the number obtained is 20. Find the value of n.

  1. A.5
  2. B.10
  3. C.15
  4. D.40
Show the answer and explanation

Answer: A (5)

Explanation

nP2 = n(n − 1) = 20, so n2 − n − 20 = 0, (n − 5)(n + 4) = 0 and n = 5.