1990乘198.9减1989乘198.8等余?4.4乘18加0.56乘165要简便运算啊

1990乘198.9减1989乘198.8等余?4.4乘18加0.56乘165要简便运算啊
1990乘198.9减1989乘198.8等余?
4.4乘18加0.56乘165
要简便运算啊

1990乘198.9减1989乘198.8等余?4.4乘18加0.56乘165要简便运算啊
1990x198.9-1989x198.8
=199x1989-1989x198.8
=(199-198.8)x1989
=0.2x1989
=397.8
4.4x18+0.56x165
=4.4x18+5.6x16.5
=4.4x16.5+4.4x1.5+5.6x16.5
=(4.4+5.6)x16.5+4.4x1+4.4*0.5
=165+4.4+2.2
=171.6

1990*198.9-1989*198.8
=（2000-10)*198.9-(2000-11)*198.8
=2000*198.9-1989-2000*198.8+198.8*11-----提取公约数2000
=2000*(198.9-198.8)-1989+198.8*(10+1）
=200-1989+1988+198.8--优先计算简单的
=...

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1990*198.9-1989*198.8
=（2000-10)*198.9-(2000-11)*198.8
=2000*198.9-1989-2000*198.8+198.8*11-----提取公约数2000
=2000*(198.9-198.8)-1989+198.8*(10+1）
=200-1989+1988+198.8--优先计算简单的
=200+198.8-1
=34.4*18+0.56*165
=4.4*18+5.6*16.5 ---扩大缩小不变
=4.4*16.5+4.4*1.5+5.6*16.5
=(4.4+5.6)*16.5+4.4*1+4.4*0.5 --组合简单的化10
=165+4.4+2.2
=171.697.8

收起

5

1. 397.8 2. 171.6

1990×198.9-1989×198.8
=（2000-10)×198.9-(2000-11)×198.8
=2000×198.9-1989-2000×198.8+198.8×11
=2000×(198.9-198.8)-1989+198.8×(10+1）
=200-1989+1988+198.8
=200+198.8-1
=397.8 <...

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1990×198.9-1989×198.8
=（2000-10)×198.9-(2000-11)×198.8
=2000×198.9-1989-2000×198.8+198.8×11
=2000×(198.9-198.8)-1989+198.8×(10+1）
=200-1989+1988+198.8
=200+198.8-1
=397.8
第二题
4.4*18+0.56*165
=4.4*18+5.6*16.5 ---扩大缩小不变
=4.4*16.5+4.4*1.5+5.6*16.5
=(4.4+5.6)*16.5+4.4*1+4.4*0.5 --组合简单的化10
=165+4.4+2.2
=171.6

收起

第一题：
1990*198.9-1989*198.8
=（2000-10)*198.9-(2000-11)*198.8
=2000*198.9-1989-2000*198.8+198.8*11-----提取公约数2000
=2000*(198.9-198.8)-1989+198.8*(10+1）
=200-1989+1988+198.8--优先计算...

全部展开

第一题：
1990*198.9-1989*198.8
=（2000-10)*198.9-(2000-11)*198.8
=2000*198.9-1989-2000*198.8+198.8*11-----提取公约数2000
=2000*(198.9-198.8)-1989+198.8*(10+1）
=200-1989+1988+198.8--优先计算简单的
=200+198.8-1
=397.8
第二题
4.4*18+0.56*165
=4.4*18+5.6*16.5 ---扩大缩小不变
=4.4*16.5+4.4*1.5+5.6*16.5
=(4.4+5.6)*16.5+4.4*1+4.4*0.5 --组合简单的化10
=165+4.4+2.2
=171.6

收起