In this task, you're given passages that contain mentions of a time duration related quesry and we are supposed to write answer to a question that involves event “frequency", which refers to how often an event is likely to be repeated. For example, "taking showers" typically occurs ~5 times a week, "going to saturday market" usually happens every few weeks/months, etc. 
 Note that a lot of the questions could have more than one correct answers. We only need a single most-likely answer. Please try to keep your "answer" as simple as possible. Concise and simple "answer" is preferred over those complex and verbose ones.  
One example: Sentence: Namibia conducts a census every ten years. After independence the first Population and Housing Census was carried out in 1991, further rounds followed in 2001 and 2011. The data collection method is to count every person resident in Namibia on the census reference night, wherever they happen to be. This is called the de facto method. For enumeration purposes the country is demarcated into 4,042 enumeration areas. These areas do not overlap with constituency boundaries to get reliable data for election purposes as well. 
Question: How often does Namibia conduct a census?
Solution is here: every ten years
Explanation: Census is generally conducted every ten years in most countries like Namibia.

Now, solve this: Sentence: During the period from 1993 to 2011, FBI agents fired their weapons on 289 occasions; FBI internal reviews found the shots justified in all but 5 cases, in none of the 5 cases were people wounded. Samuel Walker, a professor of criminal justice at the University of Nebraska Omaha said the number of shots found to be unjustified was "suspiciously low." In the same time period, the FBI wounded 150 people, 70 of whom died; the FBI found all 150 shootings to be justified. Likewise, during the period from 2011 to the present, all shootings by FBI agents have been found to be justified by internal investigation. In a 2002 case in Maryland, an innocent man was shot, and later paid $1.3 million by the FBI after agents mistook him for a bank robber; the internal investigation found that the shooting was justified, based on the man's actions. 
Question: How many times were FBI shots not justified?
Solution:
5 cases