3.9×5.5-3.9×4.5 20-7.12-4.13-6.75 4-3.25÷1.3×0.5 25+10.2÷（8.

1.3.9×5.5-3.9×4.5
=3.9×(5.5-4.5)=3.9
2.20-7.12-4.13-6.75
=20-(7.12+4.13)-6.75
=20-(11.25+6.75)
=20-18
=2
3.4-3.25÷1.3×0.5
=4-(3.9-0.65)÷1.3×0.5
=4-(3.9÷1.3×0.5-0.65÷1.3×0.5)
=4-(1.5-0.25)
=4-1.25
=2.75
4.25+10.2÷（8.4-6.7）
=25+10.2÷1.7
=25+6
=31
5.36×10.1
=36×(10+0.1)
=36×10+36×0.1
=360+3.6
=363.6
6.8.8×1.3+1.2×1.3
=(8.8+1.2)×1.3
=10×1.3
=13
7.15×19.9
=15×(20-0.1)
=15×20-15×0.1
=300-1.5
=298.5
8.0.8×0.25×4×1.25
=(0.8×1.25)×(0.25×4)
=1×1
=1
9.7.27÷4÷0.25
=7,27÷(4×0.25)
=7.27÷1
=7.27
10.3.14×0.2+6.86×0.2
=(3.14+6.86)×0.2
=10×0.2
=2