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题库 / Prep2007E1-DS-172
If m, k, x, and y are positive numbers, is mx + ky > kx + my ?
(1) m > k
(2) x > 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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题目比较的是mx+ky和kx+my的大小，也就是mx+ky-kx-my=m(x-y)+k(y-x)=(m-k)(x-y)的大小
条件1，2单独存在不能推出(m-k)(x-y）的大小
1）+2）： m>k,m-k>0,x>y,x-y>0,所以（m-k)(x-y)>0，mx+ky>kx+my
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