2﹣÷﹣                       8.1÷（5﹣0.005×700×1）
〔1.8﹣1.8×（1.8﹣1.8）〕÷0.36        〔5﹣1.7÷（2﹣1）〕×1
             51÷+71÷+91÷
6÷〔35×（+）〕×4.8                1+3+5+7+9．