①4×(250-400÷16)
②5.5÷×
③3.6×+6.4×
④7-7×+
⑤+4.9++5.1
⑥(-0.8+)×12.5
①-+-
②×+÷
③(6﹣1.3×4)÷0.1
④0.4×0.25×8×125
⑤3.4÷[(1.25+0.45)×23]