All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Probability
Playing With Marbles (Posted on 2003-10-13) Difficulty: 3 of 5
You choose one of two identical looking bags at random. One bag has three black marbles and one white marble. The other has three white marbles and one black marble.

After choosing a bag you draw one marble out at random. You notice it is black. You then put it back and draw another marble out of the same bag at random.

What is the probability that the second marble drawn is black?

See The Solution Submitted by Ravi Raja    
Rating: 3.1000 (10 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Figuring out loud. | Comment 19 of 23 |
Bag A has marbles bbbw, bag B has bwww.
The odds of the 1st black marble being drawn from bag A was 3:4 (3 ways of drawing a black marble from A, 4 ways of drawing a black marble from the whole set of A+B).

The odds of drawing a second black marble from bag A are 3:4 times 3:4, or 9:16.
The odds of drawing a second black marble from bag B are 1:4 times 1:4, or 1:16.

Odds of drawing a second black marble from either bag are the sum of the odds for the two bags, or 10:16, which can be reduced to 5:8. Yup.
  Posted by PhatFingers on 2003-11-09 23:29:35
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (10)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information