问题
解答题
计算
（0.1+0.12+0.123+0.1234）×（0.12+0.123+0.1234+0.12345）-（0.1+0.12+0.123+0.1234+0.12345）×（0.12+0.123+0.1234）
答案
设（0.1+0.12+0.123+0.1234）=A，（0.12+0.123+0.1234）=B，则A-B=0.1，
（0.1+0.12+0.123+0.1234）×（0.12+0.123+0.1234+0.12345）-（0.1+0.12+0.123+0.1234+0.12345）×（0.12+0.123+0.1234）
=A×（B+0.12345）-（A+0.12345）×B
=AB+0.12345A-（AB+0.12345B）
=AB+0.12345A-AB-0.12345B
=0.12345×（A-B）
=0.12345×0.1
=0.012345．