Okay given that we have to take multiple factors into account: The chances of getting chest-piece 4 times in a row. 1/3 = 33.33% = 0.3333. So 0.3333 * 0.3333 * 0.3333 * 0.3333 = 0.01234 The chances of getting voidfang 4 times in a row assuming its chest-piece: 1/2 = 50% = 0.50. So 0.5 * 0.5 * 0.5 * 0.5 = 0.015625 So the chances of getting both 0.01234 * 0.015625 = 0.0001928125 0.0001928125 = 0.01928125% chance so even less of a chance based upon that assumption.