How credible is Headfirst questions?

SumitK

Friends, I am doing HeadFirst questions and I found few answers are in correct.
I searched and found same problem raised by another PMP aspirant.

The 1st and 3rd questions are wrong here at https://pmzilla.com/questions-headfirst-share-your-thoughts-pls
question 2nd is also not satisfactorily.

Harwinder, I want to trust your answer although, the above links are what I am thinking too.
Other experts can also share their viewpoint

Harwinder

Those questions are based on PMBOK Guide 3. Don't worry about them.