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题库 / Prep2007E1-DS-190
On the number line shown, is zero halfway between r and s ?
(1) s is to the right of zero.
(2) The distance between t and r is the same as the distance between t and -s.
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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条件2的两种情况, 举两个栗子:
情况A: r=-1, s= 1, t= 2, answer to target question = yes
情况B: r=-4, s=-2, t=-1, answer to target question = no
条件2出现了在不同情况下target question答案不唯一的问题, 不sufficient.
而加上条件1, 能让条件2中的情况B去掉, 这样条件2只剩下一个情况, target question答案唯一, sufficient.
条件2的两种情况, 举两个栗子:
情况A: r=-1, s= 1, t= 2, answer to target question = yes
情况B: r=-4, s=-2, t=-1, answer to target question = no
条件2出现了在不同情况下target question答案不唯一的问题, 不sufficient.
而加上条件1, 能让条件2中的情况B去掉, 这样条件2只剩下一个情况, target question答案唯一, sufficient.