Math Is Fun Forum

gozags

Member

Registered: 2007-11-11

Posts: 1

probability

Hello, I am hoping someone can help me with this problem.

An urn contains 10 balls: 4 red and 6 white.  A second urn contains 16 red
balls and an unknown number of white balls.  A single ball is drawn from each urn.  The
probability that both balls are same color is .44.  Calculate the number of white balls
in the second urn.

I have tried this to solve for the total number of balls in the second urn 4/10*16/x=.44, but get a value for x that is way too small. I have a feeling I am missing something. Any ideas anyone? Please HELP!

pi man

Member

Registered: 2006-07-06

Posts: 251

Re: probability

Let X be the number of white balls in the 2nd urn.

The chances of getting 2 white balls is 6/10 * x/(16+x).
The chances of getting 2 red balls is 4/10 * 16/(16+x).

Add the 2 together and they are equal to the .44 probability you were given.

(6x + 64) / (160 + 10x) = .44
6x + 64 = 4.4x + 70.4
1.6x = 6.4
x = 4