计算下面各题，能简算的要简算．①3.5×102 ...
计算下面各题，能简算的要简算．①3.5×102②4.28-1.39-2.61③7.2×0.3+0.3×0.8④0.4×3.14×2.5⑤840÷（0.23+0.37）÷7...
计算下面各题，能简算的要简算．①3.5×102 ②4.28-1.39-2.61 ③7.2×0.3+0.3×0.8④0.4×3.14×2.5 ⑤840÷（0.23+0.37）÷7．
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①3.5×102
=3.5×（100+2）
=3.5×100+3.5×2
=350+7
=357
②4.28-1.39-2.61
=4.28-（1.39+2.61）
=4.28-4
=0.28
③7.2×0.3+0.3×0.8
=0.3×（7.2+0.8）
=0.3×8
=2.4
④0.4×3.14×2.5
=0.4×2.5×3.14
=1×3.14
=3.14
⑤840÷（0.23+0.37）÷7
=840÷0.6÷7
=840÷（0.6×7）
=840÷4.2
=200
=3.5×（100+2）
=3.5×100+3.5×2
=350+7
=357
②4.28-1.39-2.61
=4.28-（1.39+2.61）
=4.28-4
=0.28
③7.2×0.3+0.3×0.8
=0.3×（7.2+0.8）
=0.3×8
=2.4
④0.4×3.14×2.5
=0.4×2.5×3.14
=1×3.14
=3.14
⑤840÷（0.23+0.37）÷7
=840÷0.6÷7
=840÷（0.6×7）
=840÷4.2
=200
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