The P(draw a blue marble)=0.25
The bag has:
3 blue marbles, 4 green marbles, and 5 red marbles.
This means that the total number of marbles in bag are:
3+4+5=12 marbles.
We are asked to find the probability that the marble that is randomly drawn from a bag is: Blue marble.
Let P denote the probability of an event.
We know that the probability of drawing a blue marble is equal to the ratio that the marble drawn is blue to the total number of marbles in the bag.
Hence,
[tex]\text{P(blue\ marble)}=\dfrac{3}{12}\\\\i.e.\\\\\text{P(blue\ marble)}=\dfrac{1}{4}\\\\\\\text{P(blue\ marble)}=0.25[/tex]
Hence, the answer is:
P(draw a blue marble)=0.25