简便运算：9.99x778+3.33x666，9991+999.1+99.91+9.9991，2007分之2006x2008

9.99x778+3.33x666
=9.99*778+3.33*3*222
=9.99*(778+222)
=9.99*1000
=9990
2006/2007 *2008
=2006/2007 *(2007+1)
=2006/2007 *2007 +2006/2007
=2006+2006/2007

9991+999.1+99.91+9.9991
=9991+9+0.9991+999.1+0.9+99.01
=10000+0.9991+1000+99.01
=11000+0.99+0.0091+99.01
=11000+100+0.0091
=11100.0091

9.99x778+3.33x666
=9.99*（778+222）
=9.99*1000
=9990
9991+999.1+99.91+9.991
=999.1*（10+1+0.1+0.01）
=999.1*11.11
=（1000-0.9）*11.11
=11110-9.999
=11100.001
2007分之2006x2008
=2006/2007*(2007+1)
=2006+2006/2007
=2006又2006/2007 .

9.99x778+3.33x666
=9.99x778+9.99x222
=9.99x(778+222)
=9.99x1000
=9990

9991+999.1+99.91+9.9991
=9991x(1+0.1+0.01+0.001)
=9991x1.111
=11100.001

(2006/2007)x2008
=[(2007-1)/2007]x(2007+1)
=(2007^2-1)/2007
=2007-1/2007
=2006又2007分之2006

9.99x778+3.33x666
=9.99X778+9.99x222
=9.99x(778+222)
=9990
9991+999.1+99.91+9.991(应该是这样的吧)
=(10000-9)+(1000-0.9)+(100-0.09)+(10-0.009)
=10000+1000+100+10-9-0.9-0.09-0.009
=11110-9.999
=11100.001
2006x2008 /2007
=2006x(2007+1)/2007
=2006又2007之2006

9.99x778+3.33x666=3.33x(3x778+666)=3.33x(2334+666)=3.33x3000=9990
9991+999.1+99.91+9.9991=(10000-9)+(1000-0.9)+(100-0.09)+(10-0.0009)
2007分之2006x2008 =(2007-1)(2007+1)/2007=(2007的平方-1)/2007,最后答案是2007-1/2007
我没写全，后边的就是括号拆开，然后运算就行

9.99x778+3.33x666
=3.33x3x778+3.33x666
=3.33x2334+3.33x666
=3.33x(2334+666)
=3.33x3000
9990