A woman stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.77 of her?

The scale registers the normal force "N" that's pressing up against her feet. Her acceleration (that is, the elevator's acceleration) results from the net force acting on her (Fnet), which is a combination of the upward normal force (+N), and the downward force of gravity (-mg):

Fnet = N-mg = ma

We are told that N equals 0.77 of her normal weight; that is, N=0.77mg. So:

0.77mg - mg = ma

Solve for "a":

a = -0.23g

Since the sign is negative (and since we have used the convention that "up" is the positive direction), that means the acceleration is downward.

The acceleration is A = .33g or about 3.3 m/s^2. ANS a. If you can figure out how I got this, then you know the physics...otherwise....

Down. ANS b.