There is a total of 800 people employed by the police.
800(1/4) = 800/4 = 200 people are college graduates
800 - 200 = 600 remaining people
600(5/6) = 3000/6 = 500 people are high school graduates
600 - 500 = 100 remaining people
There are 100 employees who never have a high school diploma.