Place frozen limeade concentrate into a blender container.

Measure tequila using the empty limeade can and add it to the blender.

Measure triple sec, filling the limeade can 1/3 full, and add it to the blender.

Add the juice of the fresh limes to the blender.

Turn on the blender and gradually add ice cubes, 1-2 at a time.

Allow the mixture to become slushy before adding more ice.

Continue to add ice cubes until the blender container is full of margarita.

Serve immediately in chilled glasses, rimmed with coarse salt, if desired.