The times taken, in minutes, for trains to travel between Alphaton and Beeton are normally distributed with mean 140 and standard deviation 12.
The probability that a randomly chosen train takes more than k minutes to travel between Alphaton and Beeton is 0.675. Find the value of k.
Solution
Given that the probability that the time is greater than k is 0.675, we have:
\(P(X > k) = 0.675\)
Using the standard normal distribution, we find the corresponding z-value for the cumulative probability of \(1 - 0.675 = 0.325\).
The z-value for 0.325 is approximately \(z = -0.454\).
Using the standardization formula:
\(z = \frac{k - 140}{12}\)
Substitute \(z = -0.454\):
\(\frac{k - 140}{12} = -0.454\)
Solving for k:
\(k - 140 = -0.454 \times 12\)
\(k - 140 = -5.448\)
\(k = 140 - 5.448\)
\(k = 134.552\)
Rounding to two decimal places, \(k = 134.55\).
Log in to record attempts.