123-45-67+89
=100+23-45-67+89
=100+23+89-(45+67)
=100+112-112
=100
or
123-45-67+89
=100+23-45-67+89
=100+20+3-40-5-60-7+80+9
=100+20+80-40-60+3+9-5-7
=100+100-100+12-12
=100
123-45-67+89
=100-(45-23)+(89-67)
=100-22+22
=100
这道题是简算题啊
123-45=78
78-67=11
11+89=100
123-(45+67)+89
=123-112+89
=11+89
=100