A student is trying to pick out a piece of red chalk from 3 containers.

Container 1 contains- 2 white and 1 red

Container 2 contains- 2 white and 2 red

Container 3 contains- 3 white

If the student has one chance at picking a piece of chalk, what are his chances of picking a red one?


I think it's 3/10 because he has an equal chance of picking from each box.

I'm also thinking that it could be this:


1-(1/3)(2/3)+(1/3)(2/4)+(1/3)(3/3)= 5/18

I'm interpreting this problem this way:

The student is presented with 3 containers and he/she can choose one of them. Once that one is chosen, then he/she reaches in and picks one piece of chalk. What is the probability that he/she chooses a piece of red chalk?

P(Container 1 AND Red) = 1/3 * 1/3 = 1/9
P(Container 2 AND Red) = 1/3 * 2/4 = 1/6
P(Container 3 AND Red) = 1/3 * 0/3 = 0

We add these probabilities (it's an OR situation) to get 1/9 + 1/6 = 5/18.