求助几道数学题

zxl6300

今天也在“2/3 are either cows or pigs”纠结了半天，在网上查询了之后，发现Manhattan上有人解释了一下为什么这里的“either...or...”就相当于“and”，摘录如下（地址：https://www.manhattanprep.com/gmat/forums/of-the-60-animals-on-a-certain-farm-2-3-are-either-cows-or-t3417.html）：

“the statement "2/3 are either cows or pigs" doesn't mean that there are either 40 cows or 40 pigs. it means that, if you take the cows and the pigs together, they constitute 2/3 of the animals on the farm.
in other words, cows + pigs = 40.
(i can understand your alternate reading of the problem statement; it's reasonable enough. just remember that the gmat is their playground, not yours, and so you have to play by their rules - so remember the way certain statements are written. as a postscript, i hope that future problems like this one will be purged and/or rewritten for clarity before they make it into the official question pool; it would be a shame if students miss the problem just because of its ambiguity.) ”