Problem 1:

Several complaints recently have been sent to the Gotham City police department regarding the increasing incidence of congestion on the city's streets.  The complaints attribute the cause of these traffic tie-ups to a lack of synchronization of the traffic lights.  The lights are controlled by a main computer system, and adjusting this program is costly.  Therefore, the controllers are reluctant to change the situation unless a clear need is shown.

During the past year, the police department has collected data at 1,000 intersections.  The data were compiled on a monthly basis as shown below:

Month                          Congestion Incidence

January                                    14

February                      18

March                          14

April                            12

May                             16

June                             8

July                              19

August                         12

September                    14

October                                    7

November                    10

December                    18

a.  Construct a p-chart based on the above data.

b.  Should the system be modified if, during the next three months, reports of congestion at these 1,000 intersections indicate the following:

Month                          Congestion Incidence

January                       15

February                      9

March                          11