There are 10 marbles total.
You picked a marble and replaced it 50 times, so you have:
9/50 were purple
16/50 were orange
6/50 were yellow
19/50 were green
Multiply those by the number of marbles:
10*9/50 = 1 4/5 purple, round to 2
10*16/50 = 3 1/5 orange, round to 3
10*6/50 = 1 1/5 yellow, round to 1
10*19/50 = 3 4/5 green, round to 4
2+3+1+4 = 10
So you can say that there are 2 purples, 3 oranges, 1 yellow, and 4 green marbles.