Using this link: https://ucr.gov/crime-in-the-u.s/2016/crime-in-the-u.-2016/tables/table-12 I am trying to perform a one sample t-test.

Using this link: https://ucr.fbi.gov/crime-in-the-u.s/2016/crime-in-the-u.s.-2016/tables/table-12 I am trying to perform a one sample t-test. I have used the following as my outline for performing the t-test which I created myself:

a)     Target population:

All reported homicides by rifles in the United States

b)     Research variable:  

Total Homicide by Rifle

c)     Research question:

Is the average reported Homicide by rifle's in the US more than 300 per year?

d)     Expected result:

I predict the average reported yearly homicide by rifles in the US will be more than 300 per year.  According to http://www.gunfacts.info/gun-control-myths/assault-weapons/, "Fewer than 2% of criminals that commit violent crimes used assault weapons".

I am being told:

"300 is not an average, an average means all items are added/summed and divided by the total/n.