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题库 / Prep2007E1-DS-149
If m, r, x, and y are positive, is the ratio of m to r equal to the ratio of x to y ?
(1) The ratio of m to y is equal to the ratio of x to r.
(2) The ratio of m + x to r + y is equal to the ratio of x to y.
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:（m+x)/(r+y)=x/y -> my+xy=rx+xy 得出 my=rx
条件二：（m+x)/(r+y)=x/y 可以得出 my+xy=rx+xy 进一步得出my=rx 充分
????? 不对吧。 R等于0怎么办
求解