Thực hiện phép tính: 2/3 + 1/4 + 1/5 + 1/71 - 3/7 + 2/15 + 61/28

2/3+1/4+1/5+1/71-3/7+2/15+61/28
8×15-[115-(12-5)]
100-{250÷[450-(4×125-4×25)]
100+98+96+........+2-97-95.....-1