Adjustable dumbbell

FIG. 1 is a Perspective view of an adjustable dumbbell showing my new design in a closed position;

FIG. 2 is Front view thereof;

FIG. 3 is Back view thereof;

FIG. 4 is a Right-side view thereof;

FIG. 5 is a Left-side view thereof;

FIG. 6 is a Top view thereof;

FIG. 7 is a Bottom view thereof; and,

FIG. 8 is a Perspective view of an adjustable dumbbell shown in an open position.

The broken lines in the drawings depict portions of the adjustable dumbbell that form no part of the claimed design.