The number of cars waiting at a certain residential neighborhood stoplight is observed at 6:00 a.m. on 160 different days. The observed sample frequencies are shown here: $$\begin{array} { | l | r | r | r | r | }
\hline \text { Number of cars waiting } & 0 & 1 & 2 & 3 \
\hline 60 & 60 & 50 & 30 & 20 \
\hline
\end{array}$$ Under the null hypothesis of a uniform distribution, the expected number of days we would see 0 cars is:
A)10.
B)20.
C)30.
D)40.

Question

The number of cars waiting at a certain residential neighborhood stoplight is observed at 6:00 a.m. on 160 different days. The observed sample frequencies are shown here: $$\begin{array} { | l | r | r | r | r | } 
\hline \text { Number of cars waiting } & 0 & 1 & 2 & 3 \
\hline 60 & 60 & 50 & 30 & 20 \
\hline
\end{array}$$ Under the null hypothesis of a uniform distribution, the expected number of days we would see 0 cars is:
A)10.
B)20.
C)30.
D)40.

Quizplus · Accepted Answer

Under the null hypothesis of a uniform distribution, each of the four categories (0, 1, 2, 3 cars waiting) would be equally likely. Since there are 160 days observed, the expected number of days for each category is 160 days / 4 categories = 40 days.

The Number of Cars Waiting at a Certain Residential Neighborhood