There are 3 red marbles, 5 blue marbles and 4 green marbles.
Hence total number of marbles = 12
Probablity that at least one student select green marble = 1 - Probablity that no student select a green marble.
Now the probability that no students select a green marble = (8/12)^8 = 0.039
Hence the probability that atleast one studemt select a green marble = 1-0.039 = 0.9609 ≈ 0.961
Thus the probablity that atleast one student select a green marble is 0.961