Question

Probability help

Answer 1

An urn contains 2 white and 3 red balls. Four persons a,b,c and d in this order draw a ball without replacement. One who draws a white ball wins. Find their respective chances of winning.

Answer 2

Clearly P(A) = 2/5 and then I made a tree to determine the proceeding winners in this way :
But the answer for P(B) comes out to be 4/5 which is wrong. Any ideas ?

Answer 3

Waapas JEE prep mein lag gaye kya? :|

Answer 4

dusra account kyu? :O

Answer 5

did you account for the non replacement? it doesn't look like you did on the tree

Answer 6

I've made changes to values of white and red balls after winning or losing written in brackets(W,R)

Answer 7

i'll draw a quick tree and see if I notice any discrepancies between them

Answer 8

You seem to be correct. :\

Answer 9

Sure. Thanks!

Answer 10

@L tell me something new? :)
however the answer in my textbook is 3/10 for B and 2/5 for A(which is correct)

Answer 11

Wait, the tree you drew... the game pretty much ends at the white ball, doesn't it? So if A picks the white ball up, then you have to exclude that part of the tree!

Answer 12

I have 3/10 for B as well

2/4 * 3/5 = 6/20 = 3/10

Answer 13

In other words, the only way for B to pick a ball up is when A fails to. So you only look at the right side of the tree.

Answer 14

Oh..totally neglected that (: dunno why it didn't seem obvious to me :P

Answer 15

thanks @wilsondanielle :)

Answer 16

no problem! what do you have for c and D?

Answer 17

1/5 and 1/10

Answer 18

3/5*2/4*2/3 for C
and
3/5*2/5*1/3*1/2 for D

Answer 19

Those are what I got to.
It ends up being a pattern : A = 4/10 (2/5), B = 3/10, C = 2/10 (1/5), D = 1/10

Answer 20

too*

Answer 21

yep :D beautifully