What is the probability, expressed as a decimal, of drawing one marble which is either red or blue from a bag containing 3 red, 3 blue, and 6 yellow marbles?

Number of red marbles = 3.

Number of blue marbles = 3

Total number of marbles=3+3+6=12.

Probability number of red and blue marbles out of total number.

=> 6/12

or 0.5