Are answers posted to the FAA Sample Knowledge Exams?
Let me answer your question by first quoting from the 2017 Gleim Instrument Pilot Knowledge Test book.

The FAA no longer releases the complete database of test questions to the public. Instead, sample questions are released on the Airman Testing page of the FAA website on a quarterly basis.…
Gleim utilizes customer feedback and FAA publications to create additional sample questions that closely represent the topical coverage of each FAA knowledge test. 

The rewrite removed questions that are no longer relevant to most pilots, e.g. NDBs, Colored airways, and added new questions on things like GPS, PFDs, CRM.

In addition, they now shuffle the answers for each tester, so you can’t just do things like remember that most of the answers to a group of questions is 'A'.

They supposedly cleaned up the answers on some of the calculation questions so that minor differences in measurement do not result in getting an answer that is not one of the choices. For example, in previous exams some of the charts were reproduced at 98% scale. If you didn’t correct for that you would get an answer that was midway between two selections.

They also cleaned up the questions that had two right answers but one was more right than the other.

Since the exams are testing for the same content, and draw the questions from known publications, understanding past questions will give you the knowledge to pass the current exam.

Purchasing a test book from GLeim, ASA, or Sporty’s is probably worth the money for most people. With your purchase, most booklet makers also give you on-line tests so you can go into the test well-prepared.

According to Gleim, 85% of test takers pass on the first try, so don’t make too big a deal out of the test. If you are prepared, you’ll pass.