We have learned that officially , but here the wavefunction is real so theres no difference gives us a probability density. In this case, because we are in a 1-dimensional problem, that means we get a quantity with units of 1/length. You can see that if you pull the units through when you evaluate 2. If you multiply that 1/length quantity by dL, then you get the actual probability for being within a distance dL of the point where you evaluated 2. So your answer here will include a dL term, since no suggestion is given for how big to take dL. In part (c), you are asked to imagine a particle making a transition from n = 2 to n = 3 while it is at x = 5 . Remember that you are in a 10 box, so 5 is the midpoint of the box.)