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题库 / GMATAdvanced-DS-12
A $10 bill (1,000 cents ) was replaced with 50 coins having the same total value. The only coins used were 5-cent coins,10-cent coins. 25-cent coins,and 50-cent coins. How many 5-cent coins were used?
(1)Exactly 10 of the coins were 25-cent coins and exactly 10 of the coins were 50-cent coins.
(2)The number of 10-cent coins was twice the number of 5-cent coins.
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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注意题目中还有一个条件是一共有50个硬币！！！
题目中说的这四种硬币应该是可以不一定都用到的，否则的话应该选d
第二个条件可以从平均数角度来看比较好想，50个coins 1000cents那么平均每个硬币价值20cents，四种硬币分别就是-15cents；-10cents；+5cents和+30cents
根据条件2，每有一个5cents的硬币那么前两种的价值总和为-35cents需要要么1个25的，1个50的来抵消；要么7个25的，0个50的来抵消；两个解所以B错
不要漏掉题目中提及硬币总数的条件！！
注意题目已知条件
远不止两个解。。。
不要丢掉题目中一共50 个硬币的条件
设x个5-cent coins，y个10-cent coins
已知条件(1)
x + y = 30
5x + 10y = 250
c