4 February 2020
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From New Scientist #1687, 21st October 1989 [link]
“What time is it dear?” asked old Mrs Protheroe, from her wheelchair. “Is it time for the evening news yet?” Her husband pulled the watch, on the end of its chain, from his waistcoat pocket. “Drat! It’s stopped; I must have forgotten to wind it up last night.”
“That’s no cause for you to use such strong language,” snapped his wife. “Anyway, Joanna has left her watch on the sideboard. Perhaps that’s working.”
Mr Protheroe picked up his grand-daughter’s watch and stared at it. Now he was what one might call old-fashioned: he had no truck with modern contraptions, like digital watches. His brow furrowed in concentration as, for the first time in his life, he tried to decipher the strange looking figures on the face of the watch. He turned it first one way, then the other, until, with a triumphant “Ah!”, he announced the correct time to his wife.
What Mr Protheroe did not realise was that:
(a) He was holding the watch upside-down;
(b) The watch was 21 minutes slow.
Nevertheless, the time he announced was the correct one.
What time was it?