'The reason is that the criterion used by the rational shopper is not the length of the queue, but the expected time taken to exit from the queue. Shoppers do not join a queue whose expected exit time is high, therefore slow- moving queues are short.'
The professor points out that shoppers take into account the number of people in the queue, the fullness of their trolleys, an assessment of their packing and purse-finding abilities, and any prior knowledge of the efficiency of particular check-out operators. 'Using this information, shoppers form an opinion of which queue is the fastest and then join it.'
Using this model of queue- joining behaviour, Professor Treble proves that the expected time for all queues, including the 'fewer than eight items' variety, is the same. His proofs, however, are held in a queue until next week. Professor Treble ends with a peculiarly relevant silly question of his own: Why do so many purportedly silly questions have sensible answers?
Also A S Clayden asks why the autumn and winter months have longer names than the spring and summer ones; K Knight wants to know why the inside lanes of motorways are called the outside lanes, and vice versa; and Pamela Apthorp asks why, when opening a new packet of tea, whichever end she tries first she encounters an 'open other end' note.
Following Professor Treble's question, we are extending this column to include sensible questions, which will be answered, where possible, by the in-house erudition of the Independent. Enquiries of all types should be sent to: Questions (Silly, Sensible or Uncertain, as applicable), The Independent, 40 City Road, London EC1Y 2DB.Reuse content