Practice Problems for  the Lander Math Contest
Module 2, Problems (4-6):

4) A pair of fair dice is tossed. Find the probability that at
least one die shows a 3.

5) A red bag contains 4 black and 3 white marbles. A yellow
bag contains 2 black and 5 white marbles. A fair coin is
tossed. If the coin turns up heads, a single marble is taken
from the red box. If it turns up tails, single marble is taken from
the yellow box. Find the probability that the marble taken is
black.

6) A fair coin is tossed four times. What is the probability of
having precisely two heads
?