计算2.1+4.2+6.3+8.4+10.5+...+21=几

计算2.1+4.2+6.3+8.4+10.5+...+21=几
2025-03-31 23:07:09
推荐回答(2个)
回答1:

=2.1*(1+2+。。。+10)
=2.1*(1+10)*5
=2.1*55
=115.5

回答2:

115.5