21500÷125的简便和16800÷120的简便

16800/120
=1680/12
=1680÷4÷3
=420÷3
=140
123*18-123*3+85*123
=123*（18-3+85）
=123*100
=12300
21500/125
=21500÷5÷25
=4300÷5÷5
=860÷5
=172