The unintended consequences of the new EU car speed limit

A once famous question posed to job-seekers at Microsoft was ‘Why are manhole covers round?’ The question was revealing not because there was a single right answer, but precisely because there wasn’t. It helped elicit whether the applicant was someone happy to supply one plausible answer or someone who looked beyond the obvious.

At a simple level, manhole covers are round because manholes are round. But there are other reasons. A circular manhole cover cannot fall down the hole beneath; a square manhole, if aligned diagonally, could. Round manhole covers can also be moved easily by rolling and replaced in any orientation. They are probably stronger than square ones. And so on.

Equally good is the question asked of economics students by Professor Robert Frank at Cornell. ‘What happens to the price of pork if the price of pig-feed rises dramatically?’