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斯布林教授牵着四匹马过桥。桥最多只能容纳教授和两匹马通过。已知四匹马过桥的时间分别为3分钟、5分钟、8分钟和11分钟,每次往返都需要教授骑着马引领。问:四匹马都过桥最少需要多少分钟?把四匹马记为A、B、C、D,把它们的过桥时间记作A(3)、B(5)、C(8)、D(11)。(1)4匹马过桥每次两匹,返回一匹,桥的另一头只能留下一匹。最后一次两匹马过桥后不再返回。所以,四匹马全部过桥需要过桥3次(第3次不返回)才能完成。(2)要所用时间最少,则返回的马尽量要使用A(3)或B(5)。
Professor Sibling took four horses across the bridge. The bridge can only accommodate professors and two horses at most. Four horses are known to cross the bridge for periods of 3 minutes, 5 minutes, 8 minutes and 11 minutes, each with a need to teach a horse to lead. Q: How many minutes does it take for the four horses to cross the bridge? Record the four horses as A, B, C, D, and record their crossing time as A (3), B (5), C D (11). (1) 4 horses crossing the bridge two at a time, returning one, the other end of the bridge can only leave one. The last two horses will not return after crossing the bridge. Therefore, all four horses across the bridge need to cross the bridge 3 times (the third does not return) to complete. (2) To use the least amount of time, the returned horse should use A (3) or B (5) whenever possible.