While working on a case Dr. Watson accidentally fell down a 30ft dry wishing well. Sherlock Holmes lowered him down a rope. "Can

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问题 While working on a case Dr. Watson accidentally fell down a 30ft dry wishing well. Sherlock Holmes lowered him down a rope.
"Can you climb up?" shouted Holmes.
"I’ll be out before you know it. " came Watson’s reply.

But the climb wasn’t as easy as Watson had first imagined. Each hour he managed to climb 3ft—but slipped back 2ft.
How long did it take Watson to get out?

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答案28 hours

解析 他一小时爬3ft,倒退2ft,就相当于一小时爬1ft,当他爬了27小时后,爬了27ft,那么剩下的3ft正好还需要一个小时,故共需28小时。
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