Five persons are standing on one side of a bridge.
They want to cross the bridge.

Without a torch, they cannot proceed.
Only one torch is available.
The torch has a remaining battery life of only 30 seconds.

Only two people can go over the bridge at one time.
The torch needs to be returned to the remaining persons.

The five people take different times to cross the bridge.
One takes 1 second to cross the bridge.
The others take 3 seconds, 6 seconds, 8 seconds and 12 seconds.

Everyone crosses the bridge within 30 seconds.

Question : How do they proceed?

• First, persons taking 3 secs & 1 sec will cross the bridge with torch. And person taking 1 sec stay there and person taking 3 secs will return with torch.
  Time taken for this : 3 + 3 = 6 secs
  
  Then persons taking 8 & 12 secs will cross the bridge. And both stay there and person taking 1 sec who is already there will return with torch.
  Time taken for this : 12 + 1 = 13 secs
  
  Then person taking 1 sec & 3 secs will cross the bridge. And person taking 3 secs stay there and person taking 1 sec will return with torch.
  Time taken for this : 3 + 1 = 4 secs
  
  Then at last person taking 1 sec & 6 secs wi
• 14 years agoHelpfull: Yes(5) No(2)
• Person time/sec
  A 1
  B 3
  C 6
  D 8
  E 12
  
  Side1 Side2 Time/Sec
  AB -> AB 3
  B DE 12
  A AC 6
  A AB 3
  Total time 29 sec
  
  
• 14 years agoHelpfull: Yes(2) No(0)