Virtual Arithmeticles

Mystery Math 

In this episode, the students have to find a mathematical solution to help a family of 4 cross the one-mile long bridge in 60 minutes…before the bridge collapses due to the storm!


To help students visualize the situation, they can…


Materials Needed

✅ 4 small signs (post-it)
with the numbers –
25, 20, 10, 5

✅ A flashlight (or any prop
to represent one.)


What to do

✅ Have 4 student volunteers come to the front of the class to be the Bushel family. Introduce Sylvie and put the number (5) on her shirt. Then introduce the other family members while sticking the post-it numbers on each one of them.

✅ Give the family the flashlight and explain that they must have the flashlight in hand when crossing the bridge.

✅ Explain that only 2 family members can cross at a time due to the condition of the bridge and they have exactly 60 minutes before it collapses. Then ask the students who they want to cross first (2 family members) and try it out. After they cross the room to the “other side of the bridge” ask the students how long it took the 2 of them to cross?

✅ Example – Let’s say that Robbie and his mother crossed together. Students might think that you add the numbers together (20+10) and it took them 30 minutes to cross. However, since they have only one flashlight, they must walk together (Robbie must slow down) and it took them 20 minutes one way.

✅ Now, since they can’t throw the flashlight back across the bridge (1-mile-long), one of them must cross back with the flashlight. Your students will realize that the faster one must go back.

✅ While they are trying to move the family to safety, you add the score on the board so every one can see if the whole Bushel family crosses the bridge in 60 minutes.


After trying several times your students will realize that the faster ones (Sylvie and Robbie) will be the ones who cross back with the flashlight each time.

The slower ones (the parents…20 and 25 minutes) must cross together – that is the only way you don’t have to count the 20 minutes!


Meet the Bushel Family:

● Mr. Bushel – Crosses the 1 mile long bridge in 25 minutes
● Ms. Bushel – crosses in 20 minutes
● Robbie – crosses in 10 minutes
● Sylvie – is the fastest! – 5 minutes 

The Bridge

♦  The bridge is 1 mile long.
Since it’s very old, only 2 people can cross together at a time.

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