The probability of rolling a 6 on a biased die is 1/5

Work out the probability of rolling exactly one 6

if the probability of a 6 is 1/5, the probability of "not six" is 4/5. The probability of a 6 on the first roll and not on the second is 1/5 x 4/5 = 4/25. The six could come on the second roll so that probability must be doubled. The overall probability of exactly one six is 8/25 or 0.32.