脱式计算,如果是能简便算的那就简便算.

3.97×0.5×2
=3.97×（0.5×2）
=3.97×1
=3.97
4.8×0.25
=1.2×(4×0.25)
=1.2×1
=1.2
50.4×1.9-1.8
=50.4×（2-0.1）-1.8
=50.4×2-50.4×0.1-1.8
=100.8-5.04-1.8
=100.8-（5.04+1.8）
=100.8-6.84
=93.96
9.07-22.78÷3.4
=9.07-6.7
=2.37