简便计算902-17×45
=900-17×45+2
=45×(20-17)+2
=45×3+2
=137
简便计算如下,使用拼凑法,将17转化为20-3,所以原式=902-(20-3)*45=902-20*45+3*45=902-900+135=137
902-17×45
=902-(17÷2)×(45×2)
=902-8.5×90
=902-8.5×(100-10)
=902-(8.5×100-8.5×10)
=902-(850-85)
=(900+2)-850+85
=(900-850)+(85+2)
=50+87
=137
902-17×45
=900+2-765
=900-765+2=135+2=137
902-17×45
=902-(20-2-1)×45
=902-20×45+2×45+1×45
=902-900+90+45
=2+90+45
=137