Tricky about drunkyard to fall in a pit.

In every 13 seconds he goes 3 mt forward So 12 mtrs in 52 seconds and last 8 metrs in will be into pit. So total 52+8=60

Just before he falls into the pit, he should have just covered the forward 8 metre journey. Before that, he would have already covered $20-8=12$ metres displacement. Since each round moves him forward by $8-5 = 3$ metres, moving forward by 12 metres would take him $12 \div 3 = 4$ rounds. Each round takes him $8+5 =13$ seconds, so four rounds would take him $4 \times 13 = 52$ seconds, plus 8 seconds at the end and we have exactly one minute.