0.9999乘0.7加0.1111乘2.7是多少?还有：7.5乘2.7加1.9乘2.5和8.4乘2.9减1.6乘2.1

第一个答案是0.9999
第二个是25
第三个21

0.9999 25 21

0.9999×0.7+0.1111×2.7
=0.1111×9×0.7+0.1111×2.7
=0.1111×6.3+0.1111×2.7
=0.1111×(6.3+2.7)
=0.1111×9
=0.9999
7.5×2.7+1.9×2.5
=2.5×3×2.7+1.9×2.5
=2.5×8.1+1.9×2.5
=2.5×(8.1+1.9)
=2.5×10
=25
8.4×2.9-1.6×2.1
=8.4×2.9-(10-8.4)×2.1
=8.4×2.9-10×2.1+8.4×2.1
=8.4×(2.9+2.1)-21
=8.4×5-21
=42-21
=21

10000分之9999
20分之493
21