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题库 / Prep2007E2-DS-152
A certain jar contains only b black marbles, w white marbles, and r red marbles. If one marble is to be chosen at random from the jar, is the probability that the marble chosen will be red greater than the probability that the marble chosen will be white?
(1) ~$\frac{r}{b+w}> \frac{w}{b+r}$~
(2) b – w > r
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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(1)b(r-w)+(r^2-w^2)>0-->b(r-w)+(r+w)(r-w)>0-->(r-w)(r+w+b)>0,因为r,b,w表示个数，都是正整数，所以r>w。
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