XDF数学题一道，指点一下把

rock19840717

If Ruth began a job and worked continuously until she finished, at what time of day did she finish the job?

1) She started the job at 8:15 a.m. and at noon of the same day she had worked exactly half of the time that it took her to do the waole job

2) She was finished exactly 15/2 hours after she had started

这题为啥A可以呀，题目没说是匀速在工作啊，我觉得应该是C啊，但是C得话，似乎条件1又没有用足，请教大家了

[此贴子已经被作者于2008-8-29 14:21:16编辑过]

rock19840717

自己顶一下，等待大家帮助

rock19840717

up

liwenxing

题目和是否匀速工作无关。需要理解出来的是，题目有这样一个意思：R完成这个工作的时间总是一定的。

那么看条件：

1）早晨8：15开始，到了当天中午12：00（at noon），刚好用了完成工作所需要时间的一半。

既然已知总时间是一定的，已经过去了一半且可算出来是3h45min，那么从12点再向后数这么长一段时间就可得出完工时点。该条件充分。完全不需要考虑工作是否“匀速”的问题。

2）开始工作后15/2个小时完成了工作。

开始时间未知，无法得出完工时点。

所以答案是A。

rock19840717

不用考虑啊...那要是做题时考虑到了到底怎么算