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June 2018 p61 q5
3300
In Pelmerdon 22% of families own a dishwasher.
A random sample of 145 families from Pelmerdon is chosen. Use a suitable approximation to find the probability that more than 26 families own a dishwasher.
Solution
Let the random variable \(X\) represent the number of families owning a dishwasher in a sample of 145 families. \(X\) follows a binomial distribution with parameters \(n = 145\) and \(p = 0.22\).
We approximate the binomial distribution with a normal distribution: \(X \sim N(\mu, \sigma^2)\).
Calculate the mean \(\mu\) and variance \(\sigma^2\):