Tính a) 7/12 - (-1/5) - 5/6 + 2/3 + (-1/5) b) 1/2 + (16/21 + 27/13) - (14/13 - 5/21)

a) 712−−15−56+23+−15=712+15−56+23−15=712−1012+812=512

b) 12+1621+2713−1413−521=12+1621+2713−1413+521=12+1+1=52