I’m not understanding the solution for this problem. In particular where is is said “Using that we can deduce… anywhere between 5(k+1)+1 and 5(k+1)-1 where k is an integer”

Apologies for the delayed response.

To answer your question, let there be between 8 and 12 workers. What would be the number of employees in the company?

The wording of the question is very confusing. I only understood the question after seeing the solution.

Maybe you can help us improve the problem - suggestions welcome.