#4: Bridge Riddle

This Math Minute is a fun Bridge Riddle from TEDEd.  Make sure to pause right at 2:00 and try to figure it out BEFORE the answer is given in the video.  No cheating!

How can you spend your Math Mintues this week?

  • Draw out your solution to the riddle on a piece of paper.
  • Make a video of the solution by acting it out with paper figures.
  • Leave a comment with the answer to one of the questions below:
    • Who is the slowest out of the four people in the riddle?
    • How many people can the bridge hold at a time?
    • Why does everyone crossing the bridge have to stay together?
    • Which pair should go together first?  Why?
    • Which pair should go together second?
    • Why do you have to get everyone to the other side before the zombies start to cross?
    • Why does it help to have the two slowest people together?
  • Post another riddle in the comments below.  Don’t leave the answer!  See if someone else can figure it out!

25 thoughts on “#4: Bridge Riddle

  1. If you don’t get everyone across in time the first zombie will collapse the bridge with the people on it.

  2. Two fathers and two sons sat down to eat eggs for breakfast. They ate exactly three eggs, each person had an egg. The riddle is for you to explain how.

    1. I said that the janitor and the professor should have crossed. Then you should have ran down there, grab the lamp, go back to the other side, grab the girl, go to the other side again and cut the ropes.

      1. That would have worked too Stella! Ten minutes for the professor and janitor to go, two minutes for you to run there and back to get the lantern, and then another 2 minutes for you and the assistant to run. Total: 14 minutes!

        1. The lantern has to be next to who is going across Ispady so the janitor or scientist would have to go back so it wouldn’t work.

    2. It’s me Jack from Camp Kitaki. The answer to your riddle is there is a dad, a grandpa, and a kid, so the grandpa’s kid is the dad and the dad’s kid is the kid.

    1. If both the slow ones go first Conner, that would be 10 minutes. Then someone has to bring the lantern back for the next group to get across and then it would be over the time limit!

  3. This was super hard but I did it
    So I go with the professor witch equals 10 minutes and the Janitor and the lab assistant go that equals 5 minutes witch all together equals 15 minutes.

    1. Thanks for posting Charlie! Did you figure in the time that it takes to get the lantern back to the 2nd group of people? It’s dark and they need the light! 🙂

      1. It’s easy! There are problems like this in math lands. The 1 and 2 go first with lantern, then 1 goes to bring the lantern back to 5 and 10 which makes us already 4 minutes in. Then the 5 and 10 go across together only taking up 10 minutes because of how they crossed leaving us with 3 minutes left, so when 5 and 10 get across 2 brings it over to 1 bring them both over in seventeen minutes to cut the ropes.

  4. Why do have to get to the end of the bridge before the zombies cross it? Because it can only hold two people and it will snap!

  5. Why does anyone on the bridge have to stay together? Because you need the lantern. If you were not by the lantern, you could not see and then you might walk off or turn around.

  6. 1 and 2 go then the 1 would go back and give the lantern. That would take 4 minutes. Then the 10 and 5 go and when they crossed, 2 brings it over to 1. That would take seventeen minutes so they can cut the rope.

  7. Here’s a hint: if you put the slow people first it could take up half of your time.Try to figure out the rest on your own

    1. But if you do that Ved, who is going to come back with the lantern to get the other 2 people across. It will take 10 minutes for the 2 slowest people to get across and then another 5 minutes to bring the lantern back. You’re already at 15 minutes and only 1 person is across safely.

  8. The slowest person is the professor, he takes 10 minutes to cross. The bridge can only hold 2 people at a time or it will collapse. The people on the bridge must stay together because the lantern isn’t very bright and it is very dark out. You and the lab assistant should go first so you can quickly run back to give the lantern to the slower ones. Next, the lab assistant should run back so the professor and janitor can walk across in the least amount of time. Everyone must get across before the zombies step onto the bridge or else the bridge will collapse because ther will be 2 people and 1 zombie. Only 2 people can be on the bridge at once.

  9. What if only 1 person could walk at a time and you only have 17 minutes to get across, and you don’t need the lantern?

  10. You had to have the lab assistant go first so she can run back with the lantern to give it to you after the old guys and run back together.

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