I've never heard of checkmrks indictaing that something is wrong.
Depends on the teacher. It may also be a cultural thing, but I don't know enough of teachers in other countries to say otherwise. Like I said, it's pretty obvious which questions are wrong by how your teacher marks them. Just viewing a single question with no knowledge of the teacher's style isn't enough to tell you if the red checkmark is supposed to be right or wrong.
Though, one thing that is nearly universal is that teachers tend to not mark correct answers, so there's that.
But I think it's the comments that are slaying me. Why did I even read them?
There are hundreds of comments devoted to whether or not the teacher was wrong in responding to #1. Some "gems":
"nope your wrong the number "pie" or "3.14...." doesnt end therefore it cant be divided at all"
"1, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, and 47.... all the prime numbers less than 50"
"So I can divide 1 by 2?? Wow... you must have been a super duper student..."
"Inanimate objects don't carry an apostrophe when dealing with ownership."
Plus a multitude of people saying the teacher sucked for not properly defining an even number while forgetting that this was likely a test for a freakin' first-grader who really does only need to know that a larger number can be determined to be odd or even by looking at the ones digit.
Although, #7 could have been answered by a Dominion pro.