Final answer:
The probability of rolling a blue or red side on the fair cube is 2/3.
Step-by-step explanation:
To find the probability of rolling a blue or red side on the fair cube, we need to determine the total number of blue and red sides and divide it by the total number of sides on the cube.
There are 2 blue sides and 2 red sides, so the total number of desired outcomes is 2 + 2 = 4. The total number of sides on the cube is 6.
Therefore, the probability of rolling a blue or red side is 4/6, which can also be simplified to 2/3.