1)Send the 17 and the 13.Originally Posted bybharathlece

2)After 13 min, 13-guy finished and 17-guy walked for 13 min, there is room for another.

3)Now send the 7 minute guy.

4)After 4 min, the 17-guy finished and 7-guy waled for 4 min, there is room for another.

5)Send the 3 minute guy.

6)After 3 minutes both the 3 and 4 guys finished on time.

In total 20 minutes where used.