求教GMAT数学题

vinceshieh

Is rs=rx-2?
(1) r is an odd numbe
(2) x=s+2
答案是B,但是我想不通,求教.

LuckyStars

答案对不啊？顶楼主，同不会

vinceshieh

我觉得不对,答案解释如下: 2 is suficient : restate the equation as rs=rs+2r-2, therefore 2=2r, and r=1. if r=1,then the equation above can be simplified to s=x-2, which is the same statement as 2, which we know to be true. .....
From Mraw-Hill's数学

annieview

我想2是不充分的条件。正是不知道所以字母的确切值和关系，才需要条件来确定。如果可以假设r=1那还需要条件吗？干脆直接假设等式成立了。