Solution Step 0/0
A bag contains either a red ball or a blue ball. A red ball is then dropped into the bag, so now the bag has 2 balls.
A drawing is held, and a red ball is drawn out of the bag. What’s the probability of the remaining ball also being red?
A drawing is held, and a red ball is drawn out of the bag. What’s the probability of the remaining ball also being red?
Explanations
At first it can seem the chances of a red ball remaining in the bag are 50%. But there are actually three, not two, equally possible states:1. The initial red ball (A) was drawn, leaving the added red ball (C).
2. The added red ball (C) was taken, leaving the initial red ball (A).
3. The added red ball (C) was taken, leaving the blue ball (B).
In two out of these three cases. a red ball remains in the bag. Thus, the chances are 2/3.
In the initial draw, the chances of pulling out a red ball are 3/4 (as is shown in the diagram). but once the first ball is drawn, the odds change to 2/3 as is described above.
Check 1/2
Check 2/3
Check 3/4
Check 4/5
