OG11三本书中，补充的那个数学小本。里面DS-No.38是这么说的：

Machine X runs at a constant rate and produces a lot consisting of 100 cans in 2hrs. How much less time would it take to produce the lot of cans if both machinex X and Y were run simultaneously?

1. Both machines X and Y produce the same numbers of cans per hr.

2. It takes machine X twice as long to produce the lot of cans as it takes machines X and Y running simultaneously to produce the lot.

OG给的答案是 D，我觉得倒是B。

我的理解是，题目中强调了X是constant rate. 而1中并没有提到Y也是 constant rate. 假设需要60cans,

1，如果Y不是constant rate, 10mins就生产了50个，然后后面50分钟歇着，则X,Y一起工作生产60cans的时间是X以constant rate 生产10个的时间，1/5hr=12分钟。

2，如果Yconstant rate, 则一起工作生产60的时间是：30/50hr=36分钟。

答案不一致阿。

但是B的条件是可以让答案唯一的：不管Y怎么生产，两个一起工作的总产量，X总要两倍生产时间才能完成。那么少的时间很明确。

是不是我想多了阿？大虾们？

the question requires that X and Y were run simultaneously

xy同时在工作，