When it opened the M25 was the longest ring road in Europe, completely encircling London. In the UK we drive on the left, so going clockwise around the M25 you drive on the outside carriageway, and going anticlockwise you drive on the inside carriageway.
So it is shorter to drive around the M25 in an anticlockwise direction than in a clockwise direction. But how much shorter? The M25 is 117 miles long, so surely there is quite a big difference.
Assume two white vans drive around the M25 in opposite directions, and being white vans they stay in the fast lane in the middle of the motorway. For the sake of simplicity the two lanes are always ten metres apart, and the motorway is on a flat plain.
What is the difference between the two vans' journeys?
Answer at 9.00 on Monday