(i) The three conditions for a binomial distribution are:
- Constant probability of success.
- Independent trials.
- Fixed number of trials with only two outcomes (success or failure).
(ii) Let the random variable \(X\) represent the number of days Julie's train is late out of 9 days. \(X\) follows a binomial distribution with parameters \(n = 9\) and \(p = 0.3\).
We need to find \(P(X > 7) + P(X < 2)\).
\(P(X > 7) = P(X = 8) + P(X = 9)\)
\(P(X = 8) = \binom{9}{8} (0.3)^8 (0.7)^1\)
\(P(X = 9) = \binom{9}{9} (0.3)^9\)
\(P(X < 2) = P(X = 0) + P(X = 1)\)
\(P(X = 0) = \binom{9}{0} (0.3)^0 (0.7)^9\)
\(P(X = 1) = \binom{9}{1} (0.3)^1 (0.7)^8\)
Calculating these probabilities:
\(P(X = 8) = 9 \times (0.3)^8 \times (0.7) = 0.000015\)
\(P(X = 9) = (0.3)^9 = 0.00000019683\)
\(P(X = 0) = (0.7)^9 = 0.0403536\)
\(P(X = 1) = 9 \times (0.3) \times (0.7)^8 = 0.121060821\)
Adding these probabilities:
\(P(X > 7) + P(X < 2) = 0.000015 + 0.00000019683 + 0.0403536 + 0.121060821 = 0.196\)