Among fatal plane crashes that occurred during the past 55 years, 619 were due to pilot error, 85 were due to other human error, 574 were due to weather, 566 were due to mechanical problems, and 524 were due to sabotage. construct the relative frequency distribution. what is the most serious threat to aviation safety, and can anything be done about it?

Employees at a library check out books to patrons. books have an isbn and a name. the library sometimes has multiple copies of the same book. books have one or more authors. a patron is an individual who has an active (non-expired) library card. for each library card, we store the person's first and last names and their address. for each employee, we store their employee id, current salary, first and last name and their address. we also store the employee id of their current manager. each time we check out a book to a patron we need to store the date of the transaction, the employee who checked out the book to the patron, and the library card of the patron. some employees have library cards. if an employee patron turns in a book late, the fine that they pay is a percentage of their salary. some employees are authors who have library cards—they are allowed to check out as many books as they like.