WAEC 2018 · Paper 2 · Q5

The probability that a boy wins a race is 0.8. In four different races, what is the probability that he wins:

  1. (a)

    all races;

  2. (b)

    no race?

Worked solution (try it first)
  1. The races are independent, with P(win)=0.8P(\text{win}) = 0.8 and P(lose)=0.2P(\text{lose}) = 0.2.

(a)

  1. All four: 0.84=0.40960.8^4 = 0.4096.

(b)

  1. None: 0.24=0.00160.2^4 = 0.0016.

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