The probabilities of a boy passing English and Mathematics test are x and y respectively….

Mathematics WAEC 2003

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-(x-y)+xy
  • 1-(x+y)-xy
  • 1-(x+y)+xy checkmark
  • 1 - (x - y) + x

The correct answer is: C

Explanation

Prob (passing English) = x
Prob (passing Maths) = Y
Prob (failing English) = 1 - x
Prob (failing Maths) = 1 - y
Prob (failing both test) = Prob(failing English) and Prob(failing Maths) = (1 - x)(1 - y)
=1 - y - x + xy
=1 - (y + x) + xy
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