Question

2.99+25.7和81.2-3.99用简便方法解答

简便方法哦，谢谢了~

Answer 1

2.99+25.7
=3+25.7-0.01 （原来加2.99，现在加3了，多加了0.01，要减去0.01）
=28.7-0.01
=28.69

81.2-3.99
=81.2-4+0.01 （原来减3.99，现在减4了，多减了0.01，所以要加上0.01）
=77.2+0.01
=77.21

Answer 2

2.99+25.7
=(3-0.01)+25.7
=3+25.7-0.01
=28.7-0.01
=28.69

81.2-3.99
=81.2-(4-0.01)
=81.2-4+0.01
=77.2+0.01
=77.21

Answer 3

2.99+25.7
=3+25.7-0.01
=28.7-0.01
=28.69

81.2-3.99
=81.2-4+0.01
=77.2+0.01
=77.21

Answer 4

2.99+25.7
＝(3-0.01)+25+0.7=(3+25)+(0.7-0.01)
＝28.69
81.2-3.99
=81+0.2-(4-0.01)=81+4+(0.2+0.01)
=85.21