2nd Kyū
Guide
How did you do on this one? Even though it has 10 pieces just like the first problem, many of you probably got this one right.
The reason the second problem is easier than the first is that you could use kingside castling as a pattern. Both White and Black have played O-O and there are no other pieces, so you only need to remember two elements.
This is a fairly extreme example, but the first problem used a random arrangement that could never occur in a real game, whereas the second used an arrangement that really does come up often. Incidentally, for random arrangements there is no significant difference in memory ability between grandmasters and amateurs; the accepted view is that what matters is pattern-recognition ability.
This claim is based on the results of de Groot's chess memory experiments. If you are interested, take a look at the following as well.