Dumbbell

FIG. 1 is a front, right and top perspective view of a dumbbell, showing my design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is another front, right and top perspective view thereof, in another state.

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