1. Given that we have 4 green marbles, 4 pink marbles and 5 orange marbles, let us first find the probability that we select a pink marble.
We can find this by taking the number of pink marbles and dividing it by the total number of marbles:
Pr(P) = 4/(4 + 4 + 5)
= 4/13
2. Now that we have chosen one pink marble, we must find the probability that we choose an orange marble from the remaining marbles (4 green, 3 pink, 5 orange):
Pr(O) = 5/(4 + 3 + 5)
= 5/12
3. If we want to find the probability of picking a pink marble and then an orange marble, we must multiply the probabilities we have found in the first two steps:
Pr(P)*Pr(O) = (4/13)*(5/12)
= 20/156
= 5/39
Therefor, there is a probability of 5/39 that you pick a pink and then an orange marble.