1)A bag contain 10 White balls (W) and n black ball (B). All the balls are identical. If the ball is drawn at random, the probability of drawing a black ball is 1/3. Find the value of n.
2)There are 3 white socks, 2 yellow socks and 1 red socks ina drawer.
A boy randomly takes out socks from the drawer.
a)Find the probability that the socks taken out are both white.
b)Find the probability that the socks taken out are of the same colour.
F.3Maths
2009-03-08 3:40 am
回答 (2)
2009-03-08 3:43 am
✔ 最佳答案
P(black ball) = 1/3n/(n+10) = 1/3
3n=n+10
n=5
Q2
a) P(both are white) = (3/6)(2/5) = 1/5
b) P(same in colour) = P(both are white or both are yellow)
= (3/6)(2/5) + (2/6)(1/5)
= 4/15
2009-03-07 20:06:29 補充：
下面果個第一題做錯既，
因為1/3 吾係白波probability
2009-03-08 3:44 am
1)
P(Drawing a white ball)
= 10/(10+n)
SO 10/(10+n)=1/3
n=20
2a)The required probability
=1/2 * 2/5
=1/5
b) The required probabilty
= 1/5+1/3*1/5
=4/15
P(Drawing a white ball)
= 10/(10+n)
SO 10/(10+n)=1/3
n=20
2a)The required probability
=1/2 * 2/5
=1/5
b) The required probabilty
= 1/5+1/3*1/5
=4/15
收錄日期: 2021-04-13 16:29:29
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