167 If x, y, and z are integers and xy + z is an odd integer, is x an even integer? (1) xy + xz is an even integer. (2) y + xz is an odd integer. ans:(A) 我只會用列舉的方式 這樣要花太長的時間 不知道有沒有其他作法呢? 170 If n and t are positive integers, what is the greatest prime factor of the product nt ? (1) The greatest common factor of n and t is 5. (2) The least common multiple of n and t is 105. ans:(B) 謝謝:) --

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