[問題]新PP test1 DS

[doggyface922]

DS
Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it. If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1) The probability that the ball will both be white and have an even number painted on it is 0.
(2)The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2.

答案是E...我選A

想法是....
條件ㄧ指出同時是白球且數字為偶數的機率為零，表示白球都是奇數，而球共有25顆，表示白球共有五顆，且數字為1,3,5,7,9. 其餘紅球跟籃球各十顆，數字為1 to 10。 題目求選到白球或偶數的機率， 不就是 P(白) + P(偶數)- P(白且偶數)= 5/25 + 10/25 -0 = 15/25 嗎.......

請大家幫忙解答一下...謝謝

[yoyu.tw]

DS
Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it. If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1) The probability that the ball will both be white and have an even number painted on it is 0.
(2)The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2.

答案是E...我選A

想法是....
條件ㄧ指出同時是白球且數字為偶數的機率為零，表示白球都是奇數，而球共有25顆，表示白球共有五顆，且數字為1,3,5,7,9. 其餘紅球跟籃球各十顆，數字為1 to 10。 題目求選到白球或偶數的機率， 不就是 P(白) + P(偶數)- P(白且偶數)= 5/25 + 10/25 -0 = 15/25 嗎.......

請大家幫忙解答一下...謝謝

（1）說明 白ㄉ上面不會是偶數 ＝＞資訊不夠 答案BCE其中一個
（2）P(白)-P(偶)＝0.2 ==>不知道 各式多少 無解 CE 選一個
(1)+(2) 題目沒有說數字不能重複
so你怎麼能確定 白色為五顆球 說不定 25個球上面都是 奇數 或都是偶數
＝＝＝＞選(E)

如有不正確 敬請指教^^

[doggyface922]

我了解了....
因為把 "數字不能重複" 的條件自動放了進去....
如果題目沒說明，的確是"E"....
謝謝嚕....