Here is a single image that summarizes why I recommend everyone to prepare for the ACT by practicing with official ACT tests.

 
Here is a link to the playlist of video explanations to all of the math questions in the 2019 June ACT (Form B02) Test.

 
Here is a link to the playlist of video explanations to all of the math questions in the 2019 April ACT (Form B04) Test. The math section in the 2019 April ACT test was harder than usual, and this is clear from the scoring scale, which shows that one can miss 6 questions and still score a 34 on the mathematics. In the past, typically missing 4 questions would lead to a score of 34 on the ACT’s math section. With the increasing popularity of ACT, more of the traditional SAT takers have shifted to ACT, and as a result it has become more competitive at the upper end of scaled scores.

 
I have posted video explanations to all of the math questions in the 2018 December ACT (Form AB05) Test.

 
Beginning September 2018, international administrations of ACT test will be conducted in a computer based test (CBT) format. The test will remain the same as the paper based test conducted in the US, but it will be delivered via the computer. ACT has released a free computer based test for international students. This test is identical to the 2013 June ACT test (Form 71C). Students in the US can also use this for free practice.