Question

用简便方法计算6.5*7.7-7.6*2.1

昨天邻居问我一道小学数学题，没做出来
各位高人给帮帮忙
用简便方法计算6.5*7.7-7.6*2.1

Answer 1

直接算比较简便。
6.5*7.7-7.6*2.1
=50.05-15.96
=50.05-16+0.04
=34.09
解析：（1）7.7和7.6接近，但6.5和2.1不能凑整，所以不能凑整简算。（2）对数乘数与数乘数相加减，可通过加减法结合律进行凑整简算，不能时直接按规则运算比较简便。

Answer 2

6.5X7.7-7.6X2.1
=6.5X7.7-7.7X2.1-2.1
=8.6X7.7-2.1
=64.12

Answer 3

6.5X7.7-（7.7-0.1）X2.1
=7.7X（6.5-2.1）+0.1X2.1
=……

Answer 4

6.5X7.7-7.6X2.1
=6.5X(7.6+0.1)-7.6X2.1

=6.5X7.6+6.5X0.1-7.6X2.1

=7.6(6.5-2.1)+6.5X0.1

=7.6X4.4+6.5X0.1

=7X4 + 7X0.4 + 0.6X4 + 0.6X0.4 +0.65

=28+2.8+2.4+0.24+0.65

=34.09

^_^

Answer 5

#include<stdio.h>
void main()
{
printf("%lf",(6.5*7.7-7.6*2.1));
}