1. The problem statement, all variables and given/known data why is the mean square radius of a sphere given as <r2> = 3/5 R2 3. The attempt at a solution i saw this thread https://www.physicsforums.com/showthread.php?t=293397 but i don't understand the helper (malawi_glenn)'s post he put in a p(r), but what is that? density? thanks!