so the bag contains all the color marbles, which means you have to add all the marbles together..
8+12+16= 36
there are 8 green marbles from all the marbles together, that forms a fraction of
8 / 36,that fraction can be simplified by dividing both 8 and 36 by 4
looking like
8/4 over 36/4
which will give you
2/9.!! That is the probability of a person reaching into the bad and randomly selecting a green marble.! Hope this helps!