posted by Sharon .
A box of marbles contains an equal number of red marbles and yellow marbles but twice as many green marbles as red marbles. Draw one marble from the box and observe its color. Assign probabilities to the elements.
red marbles : x
yellow marbles : x
green marbles : 2x
prob(a red marble) = x/4x = 1/4
prob(a yellow marble) = x/4x = 1/4
prob(a green marble) = 2x/4x = 1/2
notice (1/4 + 1/4 + 1/2 = 1)