Explanation:
"with replacement" is important.
that means that the mixture of the marbles and therefore the chances to pull certain marbles does not change with the previous pull.
a probability is always
desired cases / totally possible cases
we have 14 marbles in the bag
4 orange
2 green
8 purple
the probability to pull an orange marble is therefore
4/14 = 2/7
the probability to pull a green marble is therefore
2/14 = 1/7
the probability to pull a purple marble is therefore
8/14 = 4/7
a.
a green marble is pulled AND then a purple marble is selected.
we need to combine both probabilities for one combined event :
1/7 × 4/7 = 4/49
b.
a purple marble and then a green marble is selected.
4/7 × 1/7 = 4/49
since we replace the marbles after every pull, both probabilities are the same, of course.
every pull has the same probability for each desired event.
c.
2 orange marbles are selected.
2/7 × 2/7 = 4/49
d.
2 non-orange marbles are pulled
there are 10 non-orange marbles. so this is
10/14 × 10/14 = 5/7 × 5/7 = 25/49