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题库 / GMATLA-DS-12
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?
(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and $0.29 stamps.
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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根据15的倍数和29的倍数，只看个位数，加一起得到0的结果只有2种可能：15取尾数5，同时29取尾数5或者15取0同时29取0
15的倍数个位只可能是0或5；9的倍数就多了0到9都可能
假设15x个位是5，9y的个位就只能是5，y＝5，检验不可能得到x为整；y＝15，已经比440多了，排除
15x的个位只能是0，9y的个位只能0，y不能是0，y＝10只有一种可能
(1) She bought $4.40 worth of stamps --> 15x+29y=440. Only one integer combination of x and y is possible to satisfy 15x+29y=440: x=10 and y=10. Sufficient.
(2) She bought an equal number of $0.15 stamps and $0.29 stamps --> x=y. Not sufficient.
Answer: A.
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