7th Grade Math: Problem of the Week
7th Grade Math: Problem of the Week
Jen Pratt
Monday, October 15, 2018

This week a number of the 7th graders practiced their problem solving skills by solving the TedEd Bridge Riddle. The students watched a short animation describing the task (link provided), were asked to identify the important information, record the question, make a plan to solve, use and adjust their plan, share the solution, and reflect on their answer and the process.

Here is an example of the first two steps of a write-up...

The Bridge Riddle

By Tessa

Step 1:  

You, a janitor, a lab assistant, and an old professor are being chased by zombies. There is only one way to safety, and that is a bridge. You take one minute to cross the bridge, the lab assistant takes two minutes to cross, the janitor takes five minutes, and the old professor takes a very slow ten minutes to cross. The professor has figured out that the zombies will catch up to you in 17 minutes, and you have that amount of time to cross the bridge with everyone in your group and cut the ropes.

This may seem easy, but there’s a catch, only two people can cross the bridge at a time. If any more are on the bridge, it will snap and everyone will fall to a very untimely death. It is also very dark and there is only one lantern. One person must hold the lantern at all times. If you don’t have the lantern, then you can wait at either side of the bridge, or stay directly behind the person with the lantern.

Finally, you can’t do anything fancy. You can’t give the old professor a piggy-back ride just to go faster. You cannot use the bridge as a raft, make a rope swing, or befriend the zombies.

So here is the final question. How can all members of your group get across the bridge in 17 minutes before the zombies attack?

Step 2:

I plan on drawing a diagram and doing guess and check. Another time when I did this problem, I used pencils to simulate the bridge and little figurines for all of the people.

We encourage you to give the riddle a try! If you would like to check your solution, please seek out one of our expert 7th graders.