To find the probability that the standard is exceeded on at least one day, you need to calculate the complement of the event that the standard is not exceeded on any day.
The probability that the standard is not exceeded on any day is when \(X = 0\), so \(P(\text{standard not exceeded on any day}) = P(X = 0) = 0.31\).
Therefore, the probability that the standard is exceeded on at least one day is given by:
\[P(\text{standard exceeded on at least one day}) = 1 - P(\text{standard not exceeded on any day}) = 1 - P(X = 0) = 1 - 0.31 = 0.69\]
So, the probability that the standard is exceeded on at least one day is 0.69.