Question

小明去旅游了七天,月份和日期之和是84,问小明是几号回来的?

Answer 1

设月份为x,旅游第一天的日期为y,接下来六天的日期为：y+1,y+2,y+3,...,y+6则：x+y+(y+1)+(y+2)+(y+3)+...+(y+6)=84x+7y+(1+2+3+...+6)=84x+7y+21=84x=7(9-y)所以：x为7的倍数而x只能取值1,2,3,...,12所以：x=7所以：...