In the game of Chuck-a-Luck we throw three dice, each with six sides numbered 1 through 6. Players bet a dollar on a number. If the number does not come up, the dollar is lost. If the number comes up one or more times, the player wins as many dollars as there are occurrences of the number.
Compute the probability that
a) There are at least two 1's showing
b) All three dice are 1
c) There is exactly one 1 showing