①#(-)÷
②# 8.8-6.75+9.2-0.25
③÷(-)×
④÷[(-)×)]
5和9
12和30
17和51
15×60= 640÷40= ÷ = 398÷202≈ 6.9÷0.1=
1.05-0.65= 0.8×125%= 5- = ÷6= 910-430=