A nickel is tossed 20 times in succession. Every time that the nickel comes up heads, a dime is tossed. Let X count the number of heads appearing on tosses of the dime. Determine Pr{X = 0). Solution For head not to appear on the dime, there are two possibilities. 1) Nickel comes up tails P = 1/2 2) Nickel comes up heads and dime comes up tails. P = 1/2 * 1/2 = 1/4 Total Probability = 1/2 + 1/4 = 3/4 As the total 20 tosses are independent, total probability = (3/4)^20 = 0.00317.