I personally found the first one to be the trickiest, quite a bit of thinking with a colleague before we saw Pascal’s triangle in the problem. I was a bit worried that things would get trickier from there on. It surely didn’t.
The second, summing certain lines taken from files matching certain glob patterns, was easily solved with a short Haskell program.
The third, a routing problem was probably the easiest and I think most easily solved on paper. I did make a mistake though, which I caught before typing my answer into the webform.
The fourth one, adding sequences of primes, was fairly straight forward. I think it would have presented a bit more trouble if I didn’t make use of Haskell’s laziness and support for infinate lists though.