Challenge: Nose weight of the centre-axle trailer

Everyone in the queue at the Praxis shouts the same answer: '75 kilos, right?' The CBR exam designer knows you have picked up that number somewhere — and counts on exactly that. The book has no 75 kg. It gives a rule with TWO branches: a ceiling under 750 kg, a floor above it. Once you know which branch applies when, you see through every '75 kg' trap.