Your answer is 4/5, which is 80% or 0.8
If there are 20 marbles in total in the bag, and 4 blue ones, that means that the probability of taking a blue one is 4/20.
This means that the probability of not taking a blue one is 1 - 4/20, or 20/20 - 4/20, which equals 16/20 = 4/5
I hope this helps! Let me know if you have any questions :)
