How Should the Nurse Calculate a Patient's Mean Arterial Pressure

How should the nurse calculate a patient's mean arterial pressure (MAP) ?

A) Divide the systolic pressure by the diastolic pressure.
B) Average three of the patient's blood pressures over a 6-hour period.
C) Divide the diastolic pressure by the pulse pressure.
D) Add the systolic pressure and two diastolic pressures and then divide by 3.