A bus depot compares its two routes. Route P carries 5,400 passengers a day and route Q carries 3,600. The depot officer argues that route P is the more crowded of the two and should be given the depot's one spare bus. Route P is at present worked by 18 buses and route Q by 8. Which of the following is an assumption the officer's argument requires?

Crowding is felt in a bus, not on a route, and the officer offers only route totals. Spread over the fleets, route P carries 300 passengers for each bus and route Q carries 450, so the assumption the argument needs is one the figures themselves refute. That the spare bus is serviceable is a practical requirement rather than a step in the reasoning, and journey length and the number of localities do not join a daily total to crowding.