（2013•东莞）用简便方法计算①237×45+347×45-0.8②（27-15）×7×5③2.1×2.6+7.4×5.4+2.6×3.3④86.7×0.356+1.33×3.56．

Question

（2013•东莞）用简便方法计算  
①2(3)/(7)×(4)/(5)+3(4)/(7)×(4)/(5)-0.8            
②（(2)/(7)-(1)/(5)）×7×5
③2.1×2.6+7.4×5.4+2.6×3.3          
④86.7×0.356+1.33×3.56．

Answer 1

①2(3)/(7)×(4)/(5)+3(4)/(7)×(4)/(5)-0.8 
=2(3)/(7)×0.8+3(4)/(7)×0.8-0.8 
=（2(3)/(7)+3(4)/(7)-1）×0.8
=5×0.8
=4；

②（(2)/(7)-(1)/(5)）×7×5
=(2)/(7)×7×5-(1)/(5)×7×5
=10-7
=3；

③2.1×2.6+7.4×5.4+2.6×3.3 
=（2.1+3.3）×2.6+7.4×5.4
=5.4×2.6+7.4×5.4
=（2.6+7.4）×5.4
=10×5.4
=54；

④86.7×0.356+1.33×3.56
=8.67×3.56+1.33×3.56
=（8.67+1.33）×3.56
=10×3.56
=35.6