This app was mentioned in 2 comments, with an average of 2.50 upvotes
tough question I surfed so many websites, what I did actually is simply google the following "CompTIA a+ exam practice" and solve whatever list of questions I can get, although I remember two of the exam sites that I went throught :
https://play.google.com/store/apps/details?id=com.crucialexams
I actually used this Crucial Exams app. It's got a few short practice tests, and flash cards. Helped a lot for me.
https://play.google.com/store/apps/details?id=com.crucialexams