(x - 95)/5 + (x - 80)/10 + (x - 76)/80 + (x - 48)/13 = 0
1040(x - 95) + 520(x - 80) + 65(x - 76) + 400(x - 48) = 0
1040x - 98800 + 520x - 41600 + 65x - 4940 + 400x - 19200 = 0
2025x = 0 + 98800 + 41600 + 4940 + 19200
2025x = 164540
x = 164540 : 2025
x = 32908/405
Vậy S = {32908/405}