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题库 / Prep2007E1-DS-22
Of the 800 sweaters at a certain store, 150 are red. How many of the red sweaters at the store are made of pure wool?
(1) 320 of the sweaters at the store are neither red nor made of pure wool.
(2) 100 of the red sweaters at the store are not made of pure wool.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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仅看表达（1）320件毛衣既非纯羊毛，也非红色，可知480件毛衣要么纯羊毛，要么红色，要么红色纯羊毛，但是无法得知纯羊毛非红色的件数；仅看表达（2）100件毛衣不是纯羊毛的，可知剩下700件都是纯羊毛，而有150件是红色，那么150+700-800=50；这超出的50件就是红色纯羊毛。这是典型的“Pigeonhole principle”（鸽巢原理，或称抽屉原理）的应用。
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