See if you can answer this fish riddle. Imagine you’re a cargo driver who has agreed to transport several tanks of a critically endangered fish species to a new aquarium. Unfortunately, as you’re passing through shark-infested waters, the boat is battered by a fierce storm, tossing your cargo overboard. There’s one rescue sub at your disposal, but you only have enough fuel for one trip to the ocean floor. Before deciding to rescue them, you need to know where the tanks are so you can gather them all in one quick pass. Not a single fish can be lost.

Now you’ve decided to scan the three sectors of the ocean floor where the cargo could have landed. So, with the help of thermal imaging, sonar data and your shipping notes, you come up with the following information.

  1. There are 50 creatures in total that includes deadly sharks outside the tanks and fish inside.
  2. Each sector has anywhere from 1 to 7 sharks, and no two sectors have the same number of sharks.
  3. Each tank has an equal number of fish.
  4. In total, there are 13 or fewer tanks.
  5. Sector alpha (the first sector) has 2 sharks and 4 tanks in it.
  6. Sector beta (the second sector) has 4 sharks and 2 tanks.

So how many fish tanks are there in sector gamma (the third sector)? Refer to TED-Ed’s video below for answer.