Answer:
18.75
Step-by-step explanation:
80 = 100%
1% = 100%/100 = 80/100 = 0.8
the grades changed by 95 - 80 = 15.
how many % is that ?
we find the answer by checking how often 1% fits into 15. and we do this kind of check by division :
15 / 0.8 = 18.75
so, the grades changed by 18.75%.