I just got my permit the other day in MS. All I had to take was the Combination part because I already had a class B with Airbrakes. I studied maybe for 3 nights using this sites practice test. Every question I had on the practice tests were pretty much the exact questions on the test. I missed one out of 17. It stopped at 17 instead of 20 because I could miss the last 3 and still pass.
Often test systems are set up such that once a person answers 80% of the questions correctly, the test automatically gives a passing score. Test complete! Congratulations!