Question

时钟1时敲1下,2时敲2下,3时敲3下.,每隔半个小时敲一下

Answer 1

(1+12)+(2+11)+(3+10)+...+(6+7)+12

= (1+12)*12/2+12

=13*6+12

=78+12

=90

一昼夜24小时

90*2=180

答:一昼夜共敲180下