In a blender, combine limeade, orange juice, and grapefruit juice. Blend on high to puree any of the remaining pulp.
While the blender is running, add ice cubes, a few at a time, and cover quickly to avoid splashing. Continue blending until you get the desired consistency.
For a thicker margarita, add more ice cubes. For a thinner margarita, add fewer ice cubes.
Pour into your rimmed glasses and garnish with a slice of lime.
*Optional– serve with a shot of your favorite tequila, and your guests can pour it over their drink