The outside “clip‐on” lanes of the Auckland Harbour Bridge are to be closed to heavy vehicles, due to
structural damage.
Suppose in order to understand the amount of cargo being transported over the bridge that Land
Transport monitored the traffic for 16 randomly selected one hour periods. The number or trucktrailers
were counted for each one hour period and the sample mean x calculated.
Assume the number of truck‐trailers crossing the bridge per hour is normally distributed with a mean
50 and standard deviation of 8.

Define your variable.

Let X be the number of trucks/trailers using the bridge in the 16 hours sample.

X ~ N(50, 8^2)

You are to find P(X < 47).

Convert this X value to a z value by using:



Then look up your z table for the probability associated with this z value.

Extremely helpful in confirming my analysis of problems. Thank you