If I got a 28% on a test and my grade is an 88% he would that affect my grade?

Add 28% and 88%, which will give you 116%. This is over the normal grading percentage, so you have to divide by 2 because you are trying to find the percentage between two numbers. This will give you 58% as the final grade percentage.

If its from one test it doesnt always affect your grades but if you are continuously getting 28% then it will badly affect your grades