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WAEC Mathematics 2003 Question 40

Question 40

Probability

The probabilities of a boy passing English and Mathematics test are x and y respectively. Find the probability of the boy failing both tests

  1. A.1 − (x − y) + xy
  2. B.1 − (x + y) − xy
  3. C.1 − (x + y) + xy
  4. D.1 − (x − y) + xy
Show the answer and explanation

Answer: C (1 − (x + y) + xy)

Explanation

P(fail both) = (1 − x)(1 − y) = 1 − x − y + xy = 1 − (x + y) + xy.