168.1除（4.5乘2减0.8）简便 31减[0.5乘(6减5.7）加18]简便

168.1÷（4.5乘0.2减0.8）
=168.1÷（0.9-0.8）
=168.1÷0.1
=1681
31减[0.5乘(6减5.7）加18]
=31-[0.5×0.3+18]
=31-18-0.15
=13-0.15
=12.85
360÷15减2.5乘1.6
=360÷3÷5-2.5×4×0.4
=120÷5-10×0.4
=24-4
=20
[ (6.1减4.6）÷0.8减1]乘0.4
=[1.5÷0.8-1】×0.4
=[15/8-1]×0.4
=7/8×0.4
=0.35