Each day Annabel eats rice, potato or pasta. The probability that she eats potato is 0.15.
Find the probability that Annabel eats potato on more than 44 days in a year of 365 days.
Solution
The problem can be modeled using a binomial distribution with parameters:
- Number of trials, \(n = 365\) (days in a year)
- Probability of success, \(p = 0.15\) (probability of eating potato)
The mean \(\mu\) and variance \(\sigma^2\) of the binomial distribution are given by:
\(\mu = np = 365 \times 0.15 = 54.75\)
\(\sigma^2 = np(1-p) = 365 \times 0.15 \times 0.85 = 46.5375\)
We approximate the binomial distribution with a normal distribution \(N(\mu, \sigma^2)\).
To find the probability that Annabel eats potato on more than 44 days, we standardize the variable:
\(P(X > 44) = P\left( Z > \frac{44.5 - 54.75}{\sqrt{46.5375}} \right)\)
\(= P(Z > -1.5025)\)
Using the standard normal distribution table, \(P(Z > -1.5025) = 0.933\).
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