write 515% = 3/10 as a mixed number or fraction. answer in simplest terms

well, 515% is not 3/10

515% = 5.15 = 5 15/100 = 5 3/20 or 103/20

Not sure what you want to do with the 3/10. If your typo meant +, then just note that 3/10 = 6/20.