Answer: 11.5%
Explanation:Since 1 minute = 60 seconds, we multiply 12 minutes by 60 so that 12 minutes = 720 seconds. Thus, we're looking for a probability that the auditor will spend more than 720 seconds.
Now, we get the z-score for 720 seconds by the following formula:

where

So, the z-score of 720 seconds is given by:

Let
t = time for the auditor to finish his work
z = z-score of time t
Since the time is normally distributed, the probability for t > 720 is the same as the probability for z > 1.2. In terms of equation:

Hence, there is
11.5% chance that the auditor will spend more than 12 minutes in an invoice.