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17.5*2.1/3.5脱式计算

1+2+3+4+5+6+7...+15+17+19 =(1+19)X[(19-1)÷2+1]÷2 =20X10÷2 =100

5/17-4/51+2/3 =15/51-4/51+2/3 =11/51+2/3 =11/51+34/51 =45/51 =15/17 望采纳

(1)17.5÷12.5×1.4,=1.4×1.4,=1.96;(2)1.58×99+1.58,=1.58×(99+1),=1.58×100,=158;(3)4.38÷0.125÷8,=4.38÷(0.125×8),=4.38÷1,=4.38;(4)6.4×4.5+3.6×4.5,=(6.4+3.6)×4.5,=10×4.5,=45.

(1)17.5-5.15-1.85=17.5-(5.15+1.85)=17.5-7=10.5 (2)800×0.7×0.125=0.7×(800×0.125)=0.7×100=70(3)3.54×0.14-0.14×2.54 =0.14×(3.54-2.54)=0.14×1=0.14 (4)4.1×9.9=4.1×(10-0.1)=4.1×10-4.1×0.1=41-0.41=40.59

17.5÷5+6.5x2 =35+13 =48 谢谢,请采纳

20分之17-5分之2-10分之1 =20分之17-20分之8-20分之2 =20分之7

解: 1+3+5+7…+17+19 =(1+19)×10÷2 =20×10÷2 =100 方法提示:根据和=(首项+未项)×项数÷2,先分别求出它们的和,再求总和。

(3/8×5/17)×34=15/4

(1)14-7.2-2.8 =14-(7.2+2.8)=14-10=4; (2)5.5×17.3+6.6×5.5+0.1×5.5=5.5×(17.3+6.6+0.1)=5.5×24=132;(3)13.7÷12.5÷0.8=13.7÷(12.5×0.8)=13.7÷10=1.37.

=(1+19)x19÷2 =190

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