# Probility

• Jan 13th 2013, 12:01 PM
tahirakw
Probility
A bag contains 3 orange, 3 red, and 2 black balls. Two balls are to be selected at random, and the first ball selected will be placed back in bag before second marble is selected. What is the probablility that both balls selected will be black? 1/8 or 1/16. I think 1/8 because it is a total of 8 balls. Am I correct?
• Jan 13th 2013, 12:07 PM
Plato
Re: Probility
Quote:

Originally Posted by tahirakw
A bag contains 3 orange, 3 red, and 2 black balls. Two balls are to be selected at random, and the first ball selected will be placed back in bag before second marble is selected. What is the probablility that both balls selected will be black? 1/8 or 1/16. I think 1/8 because it is a total of 8 balls. Am I correct?

Replacing the ball after it is drawn makes the events independent.
Therefore, multiply: $\displaystyle \left(\frac{2}{8}\right)^2$.
• Jan 13th 2013, 12:14 PM
tahirakw
Re: Probility
Thanks. so that gives me 4/64 when I reduce its 1/16?