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Nov 2020 p53 q1
3118
The times taken to swim 100 metres by members of a large swimming club have a normal distribution with mean 62 seconds and standard deviation 5 seconds.
Find the probability that a randomly chosen member of the club takes between 56 and 66 seconds to swim 100 metres.
Solution
Let the random variable \(X\) represent the time taken to swim 100 metres. \(X\) follows a normal distribution with mean \(\mu = 62\) and standard deviation \(\sigma = 5\).
We need to find \(P(56 < X < 66)\).
Standardize the variable using the formula:
\(Z = \frac{X - \mu}{\sigma}\)
For \(X = 56\):
\(Z = \frac{56 - 62}{5} = -1.2\)
For \(X = 66\):
\(Z = \frac{66 - 62}{5} = 0.8\)
Thus, \(P(56 < X < 66) = P(-1.2 < Z < 0.8)\).
Using the standard normal distribution table, find: