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Miscellaneous Exercise · Q8

Q.The number of incorrect predictions of 4 successive football matches is

(i) 81
(ii) 64
(iii) 80
(iv) 63
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There are 34=813^4=81 total ways to predict the outcomes of 4 matches; removing the single all-correct prediction leaves the count of prediction-sets that are not entirely right, i.e. "incorrect."

Product rule: if each of rr independent choices has nn options, the total number of combined outcomes is nrn^r.

  1. Each football match can be predicted to end in one of 3 ways: a win, a loss, or a draw (for the team in question).
  2. Predicting 4 successive matches independently gives a total of 343^4 possible prediction-sets.
  3. Compute 34=3×3×3×3=813^4=3\times3\times3\times3=81. …

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