In a room, there are 4 red chairs, 6 blue chairs, and 5 green chairs. If you randomly pick one chair from the room, what is the probability that it will be either red or blue?
Let's calculate the probabilities step-by-step:

1. There are a total of 4 red chairs + 6 blue chairs + 5 green chairs = 15 chairs in the room.
2. We want to find the probability of picking either a red or a blue chair.
3. There are 4 red chairs and 6 blue chairs, so there are a total of 4 + 6 = 10 red or blue chairs.
4. The probability of picking a red or blue chair is the number of red or blue chairs divided by the total number of chairs, which is 10/15.

Hence, the probability of picking either a red or blue chair is 10/15 or 2/3.