There are 18 students in a class. each day, the teacher randomly
selects three students to assist in a game: a leader, a recorder, and a
timekeeper. in how many possible ways can the jobs be assigned?
(1) 306 (3) 4896
(2) 816 (4) 5832

Amass weighing 16 pounds stretches a spring 8/3 feet. the mass is initially released from rest from a point 2 feet below the equilibrium position, and the subsequent motion takes place in a medium that offers a damping force that is numerically equal to 1/2 the instantaneous velocity. find the equation of motion if the mass is driven by an external force equal to f(t)=cos(2t).