Question

7.81乘49减78.1乘3.8加0.78乘90怎样用简便方法计算

Answer 1

7.81 X 49 - 78.1 X 3.8 + 0.78 X 90
= 7.81 X 49 - 7.81 X 38 + 7.8 X 9
= 7.81 X ( 49 - 38 ) + 7.8 X 9
= ( 7.8 + 0.01 ) X 11 + 7.8 X 9
= 7.8 X 9 + 7.8 X 11 + 7.8 X 0.01
= 7.8 X ( 9 + 11 ) + 78 X 0.001
= 7.8 X 20 + 0.078
= 156 + 0.078
= 156.078
题目有没有输入错误呢
7.81 X 49 - 78.1 X 3.8 + 0.781 X 90
= 7.81 X 49 - 7.81 X 38 + 7.81 X 9
= 7.81 X ( 49 - 38 + 9 )
= 7.81 X ( 11 + 9 )
= 7.81 X 20
= 156.2

Answer 2

把78.1和0.781都化成7.81 7.81×49+7.81×39+7.81×99 然后用分配律

追答

7.81×9对不起多打了一个