39.8-(19.8+11.5)=39.8-19.8
72×12=×1072×
3400÷25÷4=3400÷(×)
100个十10个百 0.0540% 37×0.337÷0.3
①3.8×99+3.8
②-×-
③5×(+-)
④++++
⑤× + ÷
10.05÷32≈ 4.035÷2.4≈
40.91÷51≈ 32÷32.3≈