You’re overseeing the delivery of supplies to a rebel base in the heart of enemy territory. To get past customs, all packages must follow this rule: if a box is marked with an even number on the bottom, it must be sealed with a red top. One of the four boxes was sealed incorrectly, but they lost track of which one. Can you figure out which box it is and save the day? Alex Gendler shows how.

[TED Ed]