Test Prep II - 7

[lisayang83]

a jar contains only blue white and red marbles, if one marble is to be chosen at random, what is the probablity that a red marble chosen would be greater than a blue marble?

1. r/(b+w) > w/(b+r)
2. b - r > r

Ans. A

[eced]

題目問紅的機率要>藍的 等於是問紅的值要>藍的值
這題要有點技巧
設全部共為x, x=b+r+w
(1)r/(b+w)=r/x-r > w/(b+r)=w/x-w => r(x-w)>w(x-r) => r>w 不知跟b的關係 不成立
(2)b>2r => b>r 成立
所以答案是B

[eced]

原來是你題目寫錯了
原題如下
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) r/(b+w) > w/(b+r)
(2) b-w>r

[lisayang83]

喔謝謝!
旦算法應該還是一樣 對吧 :P