Question

A bag contains 4 blue coins and 8 red coins. A coin is removed at random and replaced by three of the other color.

Part 2 out of 3
If the first coin removed is blue, what is the probability of drawing a red coin after three red coins are put in the bag to replace the blue one?

Answer 1

The probability of drawing a red coin is 11/14. You take one blue coin away leaving you with 3 blue coins, and you add 3 red coins, which leaves you with 11 red coins. You add 11 and 3, which makes 14. 11 is the red coins and out of all red and blue coins there are 11 red coins.