If l bought a 3 day Disney pass is Disney Hollywood Studios covered by it?

You should check in the page, I think it's not included

It will count as 1 day out of the pass unless u have park hopper option

Yes

1 park per day unless you have upgraded to park hopper.

Yes all Disney parks are good with pass

Yes it includes Hollywood Studios.

Yes but only 1 park per day unless you bought a park hopper ticket

Yes, you can do a park a day, but you would need a park hopper pass to do more.

I believe the pass covers all the parks just one park per day.