passwella.
Menu

WAEC Further Mathematics 2011 Question 29

Question 29

Permutations and Combinations

If 3xC2 = 15, find the value of x.

  1. A.2
  2. B.4
  3. C.5
  4. D.6
Show the answer and explanation

Answer: A (2)

Explanation

3x(3x − 1)/2 = 15, so 9x2 − 3x − 30 = 0, i.e. 3x2 − x − 10 = (x − 2)(3x + 5) = 0. x must be a positive whole number, so x = 2.