Question

A jar contains four marbles, each a different color: red,
blue, green, and yellow. If you draw two marbles from
the jar, one after another, replacing the first before
drawing the second, what is the probability of getting
a. two red marbles?
b. a red marble on the first draw and a green marble on
the second draw?
c. at least one red marble and one green marble?
d. no yellow marbles?

Answer 1

a) prob (red,red) = (1/4)(1/4) = 1/16
b) prob(red then green) = (1/4)(1/4) = 1/16
c) could be RG or GR
so prob = 1/16 + 1/16 = 1/8
(I don't see where the "at least" comes in, you are only drawing 2 and you want a red AND a green)

d) prob (no yellow, no yellow = (3/4)(3/4) = 9/16