The probability is 0.336.
To solve this, we need Binomial Probability equation for Repeated Trials.
P = nCr (p)^r (q)^(n-r)
where P = probability (unknown)
     n = number of trials (8)
     r = number of successes (1)
     p = probability of success (.20)
     q = probability of failure (0.80)
P = 8C1 (.20)^1 (.80)^7
  = 0.336