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 pro-gram 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 3 months, reports of congestion at these 1,000 intersections indicate the following:

               Month                         Congestion Incidence

January……………………..   15

February…………………….  9

March…………………….. 11