Four people are on one side of a bridge. All of them need to cross a bridge in order to escape from a pack of zombies. They have 17 minutes before the zombies arrive and all four people must be on the other side of the bridge. It is night and there is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either one or two people, must have the flashlight with them. The flashlight must be walked back and forth, it cannot be thrown, etc. Each person walks at a different speed. A pair must walk together at the rate of the slower man
Mr. Ng: 1 minute to cross
Ms. Aspell: 2 minutes to cross
Ms. Brids: 5 minutes to cross
Mr. Dybdahl: 10 minutes to cross
To solve this puzzle, we need to find the fastest way for all four people to cross the bridge within 17 minutes. Let's break down the steps to figure it out:
1. First, we need to identify the fastest and second-fastest walkers. Since Mr. Ng takes only 1 minute to cross, he is the fastest. Among the others, Ms. Aspell takes 2 minutes, Ms. Brids takes 5 minutes, and Mr. Dybdahl takes 10 minutes.
2. We should find the minimum time it takes to cross the bridge by taking pairs of people at each step. Since the pair must walk together at the rate of the slower person, we want to pair up the fastest and second-fastest walkers to make sure no time is wasted.
3. Let's consider the possible combinations of pairs and find the minimum time required for each:
- Mr. Ng and Ms. Aspell: This pair takes a total of 2 minutes to cross (Ms. Aspell takes 2 minutes) since they both walk at their own speed.
- Mr. Ng and Ms. Brids: This pair takes a total of 5 minutes to cross (Ms. Brids takes 5 minutes) since they both walk at Ms. Brids' speed.
- Mr. Ng and Mr. Dybdahl: This pair takes a total of 10 minutes to cross (Mr. Dybdahl takes 10 minutes) since they both walk at Mr. Dybdahl's speed.
As we can see, the fastest option is to pair Mr. Ng with Ms. Aspell since it takes the least time.
4. After the first pair (Mr. Ng and Ms. Aspell) crosses the bridge in 2 minutes, someone needs to bring the flashlight back to the starting side. Since Mr. Ng is the fastest, he should go back with the flashlight, which takes an additional 1 minute.
5. Now we have Ms. Brids and Mr. Dybdahl left on the starting side, and the flashlight is on the other side.
- Ms. Brids and Mr. Dybdahl: This pair takes a total of 10 minutes to cross (Mr. Dybdahl takes 10 minutes) since they both walk at Mr. Dybdahl's speed.
6. When Ms. Brids and Mr. Dybdahl reach the other side of the bridge in 10 minutes, we have successfully crossed all four people to safety within a total of 2 + 1 + 10 = 13 minutes.
By following this plan, we can ensure that all four people cross the bridge and reach the other side safely within the given time limit of 17 minutes.