394+395+396+397+398+399+400用简便方法计算

问题描述:

394+395+396+397+398+399+400用简便方法计算

394+395+396+397+398+399+400
=400-6+400-5+400-4+400-3+400-2+400-1+400
=400*7-(1+2+3+4+5+6)
=2800-21
=2779