=-3/4×0.8+1/2÷3/4=-(3/4×0.8)+1/2÷3/4=-[3/4×(1/2+0.8)]=-3/4×1.3=-0.975
1/4×4/5+1/2×4/3-4/5=4/5(1/4-1)+2/3=2/3+4/5×(-3/4)=2/3-3/5=(10-9)/15=1/15
=1/4×4/5+1/2×4/3-4/5=1/5+2/3-4/5=(2×5-3×3)/15=1/15
