这道题可以简便计算吗?
展开全部
1.9x2.5+8.1x7.5
=1.9x2.5+8.1x(2.5+5)
=1.9x2.5+8.1x2.5+8.1x5
=(1.9+8.1)x2.5+(8+0.1)×5
=10x2.5+8×5+0.1×5
=25+40+0.5
=65.5
=1.9x2.5+8.1x(2.5+5)
=1.9x2.5+8.1x2.5+8.1x5
=(1.9+8.1)x2.5+(8+0.1)×5
=10x2.5+8×5+0.1×5
=25+40+0.5
=65.5
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展开全部
399+(154+201) =399+201+154 =600+154 =754 480+325+75 =480+(325+75) =480+400 =880 78+53+47+22 = (78+22)+(53+47) =100+100 =200 91+89+11 =90+(89+11) =90+100 =190 36+18+64 = (36+64)+18 =100+18 =118 168+250+32 = (168+32)+250 =200+250 =450 85+41+15+59 =(85+15)+(41+59) =100+100 =200
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