[問題] OG PS Q 395

[jrru27]

A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box, what is the probability that the sum of the three numbers on the balls selected from the box will be odd ?

請問(1)上面underline的那句話是什麼意思 (2)就OG的解釋,為什麼和為奇數會有四種結果?

[micki]

(1) 就是當你抽出一顆球之後,會有另一個同數字的球放回箱子內.
維持箱子內還有50個奇數球和50顆偶數球.

(2) 要抽出3顆球,總和為奇數 有下列4種狀況:
a.奇數/奇數/奇數
b.奇數/偶數/偶數
c.偶數/偶數/奇數
d.偶數/奇數/偶數

[EVAN HUNG]

A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box, what is the probability that the sum of the three numbers on the balls selected from the box will be odd ?

請問(1)上面underline的那句話是什麼意思 (2)就OG的解釋,為什麼和為奇數會有四種結果?

(1)意思就是指「每拿出一顆球後，這顆球還會被放回去箱子裡(with replacement from the box)」，所以每一次拿球箱子裡面都有50顆基數球&50顆偶數球喔! 但是如果題目是without replacement from the box，拿出來後不放回箱子，意義就等同於一次伸手進去就抓三顆球

(2) 基數+基數=偶數；基數+偶數=基數；偶數+偶數=偶數
那接下來就如MICKI說的啦~

[micki]

哈哈....針對第一點, EVAN 說的才是對的哦~~

當時突然想不起來要怎麼寫,所以才會寫成那樣.... 尷尬~~