It depends on how your teacher grades. Not every class is as strong as every other, and not every test is as hard or easy. He might feel that the whole class is performing poorly and set the pass mark at 75. Or he may feel that the class is very strong, so he gives very tough tests, with 50 being a passing rate. Grading depends on a lot of factors. It's not always 90-100 for an A, 80-89 for a B, 70-79 for a C.
We aren't able to read your teacher's mind about grading. For the highest grade to be 80 means the class isn't too sharp, or the tests are very hard. One teacher I had said no test is valid if anyone gets 100--tests should be tougher than that. A percentile of 60 isn't bad--it's obviously above average. But an absolute grade of 48 doesn't look too good. If the teacher is giving you this much information about the grades of the class, I'd expect him to also be giving you estimates of how he's interpreting these results, grade-wise. So ask him.
We aren't able to read your teacher's mind about grading. For the highest grade to be 80 means the class isn't too sharp, or the tests are very hard. One teacher I had said no test is valid if anyone gets 100--tests should be tougher than that. A percentile of 60 isn't bad--it's obviously above average. But an absolute grade of 48 doesn't look too good. If the teacher is giving you this much information about the grades of the class, I'd expect him to also be giving you estimates of how he's interpreting these results, grade-wise. So ask him.