问一道PP-DS2里的题

31.    If a wire 27 meters long is cut into three pieces of three different lengths, what is the length of the longest piece?

(1)  The length of the longest piece is twice the length of the shortest piece.

(2)  The sum of the lengths of the two shorter pieces is 15 meters.
----------------------------------------------------------------------------------------------------------------------------------【答案】B
【思路】設最長為a,中間為b,最短為c, a+b+c=27,問a=?
(1)a=2c----------------------------------------------------------------------------------insufficient
(2)b+c=15, 則a=12-------------------------------------------------------------------sufficient
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条件一说最长的是最短的两倍，我觉得是sufficient的啊....因为只有12，6，9满足最长是最短的两倍啊，那如果说比如10，5，那第三段就是12，10就不是最长的，再比如14，7，那第三段就6，7就不是最短的....所以，不就是只有12，6，9，那就是12么？？