There are 4 people who need to cross a narrow bridge at night with only one torch.?

Question

There are 4 people who need to cross a narrow bridge at night with only one torch.

The four people each have different travelling times:

Person 1 crosses in 1 minute
Person 2 crosses in 2 minutes
Person 3 crosses in 5 minutes
Person 4 crosses in 10 minutes

Only two people can cross at a time and one person has to come back over the bridge to give the torch to the others still waiting to cross. A person cannot cross the bridge without having the torch or walking next to someone who has it.

While crossing, you have to use the slowest time of the two people because they have to walk the same pace.

You have to add the person who comes back to your total time.

They need to cross in 17 minutes. How?

Here's an example:

5 and 10 go over (that's 10 minutes) and then 5 comes back with the torch (that's a total of 15 minutes). Then 5 and 2 go over (that's 20 minutes---and you're already over the time limit . . . )

How can you get all four people to the other side in 17 minutes?

Note that there is a logical answer. It won't be anything like "they can throw the torch to the other side instead of walking it over", or "they can all wait till sunrise", or "why don't they jog over and increase their times", etc!

Answer 1

Person 1 takes person 4
person 1 comes back
person 1 takes person 3
person 1 comes back
person 1 takes person 2

In other words the guy with one minute takes them all.

Answer 2

1 min and 2 minutes cross total - 2 minutes
1 min returns total - 3 minutes
5 min and 10 minutes cross total - 13 minutes
2 minutes returns total - 15 minutes
1 min and 2 minutes cross total - 17 minutes

The trick is, you have to combine the 5 and 10 minute person on the same trip so there long times dont count twice.

Didnt know it already just figured it out....

Answer 3

persons 1 & 2 cross first - 2 minutes
then person 1 comes back - 1 minute
He passes the torch to persons 3 & 4 (or the5 & 10 minute folks), who cross the bridge - 10minutes
Then person 2 goes back - 2 minutes
Picks up person 1 to get on the other side, that's - 2 minutes
total of 17minutes...

Answer 4

This is the joke section
I feel like I'm in math class again
If i wanted to go to school, I'd quit smoking out the back behind the football shed.