If a fair coin is tossed four times, what is the probability of obtaining at...

FURTHER MATHEMATICS
WAEC 2014

If a fair coin is tossed four times, what is the probability of obtaining at least one head?

  • A. \(\frac{1}{2}\)
  • B. \(\frac{1}{4}\)
  • C. \(\frac{13}{16}\)
  • D. \(\frac{15}{16}\)

Correct Answer: D. \(\frac{15}{16}\)

Explanation

P(at least one head) = 1 - P(4 tails)

Let \(p = \frac{1}{2}\) = probability of head and \(q = \frac{1}{2}\) = probability of tail.

\((p + q)^{4} = p^{4} + 4p^{3}q + 6p^{2}q^{2} + 4pq^{3} + q^{4}\)

P(4 tails) = \(q^{4} = (\frac{1}{2})^{4} = \frac{1}{16}\)

P(at least one head) = \(1 - \frac{1}{16} = \frac{15}{16}\)



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