maths hw

2a) P(紅色) = 8 / (8+4+3) = 8/15
P(白色) = 4 / (8+4+3) = 4/15
P(藍色) = 3 / (8+4+3) = 3/15 = 1/5

b)設白色的幸運星應設定為 x 分 :
設定值= 2 * (8/15) + x(4/15) + (-4)(1/5) = 0

x = - 1

白色的幸運星應設定為被扣 1 分。

(a) Probability of getting white: 4/(8+4+3)=4/15
Probability of getting red: 8/15
Probability of getting blue: 3/15 = 1/5

(b) In order to make fair, the total mark should be 0.
Let x be the mark of white
8(2) + 4x + 3(-4) = 0
16 + 4x - 12 = 0
16 - 12 = -4x
x= -1

So the mark of white is -1

2010-03-27 11:48:39 補充：
(一)拿得白色的概率為
4/(8+4+3)
=4/15
拿得紅色的概率為
8/(8+4+3)
=8/15
拿得藍色的概率為
3/(8+4+3)
=3/15
=1/5

(二)若要使變得公平，總分應為零。
設x為白色的分數
所以 紅色(紅分) +白色(白分) +藍色(藍分)=0
8(2)+4(x)+3(-4)=0
16 + 4x - 12 = 0
16 - 12 = -4x
x= -1
所以白色的分數為-1