84*17-42*2+21*136

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84*17-42*2+21*136
84*17-42*2+21*136

84*17-42*2+21*136
84*17-42*2+21*136
=84*17-84+84*34
=84*(17-1+34)
=84*50
=4200

简便算法:84×17-42×2+21×136
= 21×4×17-21×2×2+21×136
= 21×68-21×4+21×136
= 21×(68-4+136)
= 21×200
= 4200