24除以1/3减56
=24×3-56
=72-56
=16
1/2*[(1/3+5/6)除以5/7｝
=1/2×[7/6×7/5]
=1/2×49/30
=49/60
49/5*7/8除以7
=49/5×（7/8÷7）
=49/5×1/8
=49/40