The ornamental design for a pair of dumbbells with rack, as shown and described.
FIG. 1 is a perspective view of a pair of dumbbells with rack showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is an exploded view thereof.
The dashed or broken lines shown in the drawings depict portions of the pair of dumbbells with rack in which the design is embodied that form no part of the claimed design.