The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific and philosophical concepts

• Readers reply: Why is sugar-free tonic water always described as ‘slimline’?

I recently made a return trip to Edinburgh from London on which both legs of the journey were either significantly delayed or cancelled. At Waverley station, a message over the public address system told us we could travel by any “reasonable” route, but what does that mean? What counts as reasonable and what doesn’t? And who decides? Grant, by email

Post your answers (and new questions) below or send them to nq@theguardian.com. A selection will be published next Sunday.