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题库 / Prep2007E1-DS-56
During a sale, a clothing store sold each shirt at a price of $15 and each sweater at a price of $25. Did the store sell more sweaters than shirts during the sale?
(1) The average (arithmetic mean) of the prices of all of the shirts and sweaters that the store sold during the sale was $21.
(2) The total of the prices of all of the shirts and sweaters that the store sold during the sale was $420.
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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(2) 15a+25b=420
因为件数只能是正整数，不能用一元二次方程有不止一个解来直接排除，用试数法。
15a+25b=420-->3a+5b=84, 84/5=16…4，b最大是16。5b=(0,5,10,15…75,80)；用84分别减5b的极大极小值，看差数是否可以被3整除，得a的极大极小值为3，23，分别对应S>t,S
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