1. The problem statement, all variables and given/known data Image: http://puu.sh/ca93V/7eb9abf342.png [Broken] 2. Relevant equations Ok I know to use this guy http://puu.sh/ca95c/ad0155a4d6.png [Broken] Which then turns into this http://puu.sh/ca96W/68802e045c.png [Broken] (except from .5a to 4a, not 0 to a) 3. The attempt at a solution I get lost on trying to integrate this thing. All these problems involving radial probability densities seem to have weird integrals. I've tried letting x = r/a but that also just gets weird. If I could get an explanation on this topic I'd really appreciate it.