So my 2 ACT prep books seem to have different scoring guidelines, and I’d like to see if anyone can clear this up for me.
The McGraw-Hill book says missing 10 questions on the math section is a 30 composite (that number was found by multiplying the raw score by 36, then dividing that number by 60. So, 50*36/60= 30.) My Barron’s test prep book says missing 10 math questions would be a 28 (they just have a conversion chart that doesn’t show any of the actual math, just composites based on how many questions missed.) This seems like a pretty big difference in scores, so I was wondering if anyone knew which was more correct. (I would guess Barron’s is right, although I’d like McGraw-Hill to be right, because I think I missed about 10 questions on the last ACT math section, and I’d definitely rather a 30 than a 28 
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Each test has a different curve. It depends on how difficult the problems are on that particular test. Missing 10 could be 28 or 30 or some other number.
There are a lot of ACT tests and tests are used over the years multiple times. The number correct to reach any particular section score can vary from test to test. For example, there are some tests where 1 wrong in science drops you to 34 and 2 incorrect to 32. Nevertheless, 8 incorrect in math to get 30 is far more common than 10.