I know its not a direct ans to your question but I know that these tests are marked on a sliding scale of 1 - 10. NATS expect a prospective ATCO to get some where between 5 & 8. Not entirely sure how they're marked but I suppose you could read into that you need 50% - 80% overall so therefore could still pass with only answering half the questions but getting them all correct. The mark scores are correct the method of marking speculative. How do I know this, they bring it up if you every get in the situation of having a training review.
For the record I got 10, 10, 9, 6, the 6 being for the cubes which I didn't complete.