Ajar contains five red marbles and three green marbles. a marble is drawn at random and not
replaced. a second marble is then drawn from the jar. find the probability that the first marble is red and the second marble is green.

The jar starts out with 8 marbles in it. Five of them are red.
If you don't peek, the probability of drawing a red marble is

                 5/8 .

If you have already drawn a red marble on the first try, then
at that point, the jar has only 7 marbles in it, and three of them
are green.  Now, for your second draw, if you don't peek, the
probability of drawing a green marble is

                  3/7 .

The probability of BOTH of those events being successful is

               (5/8) x (3/7) = 15/56  =  approx 26.79% .