What is hiding in the jar?

This jar is full of marbles, but a cloth covers it and you are not allowed to peek. You can only shake out a few marbles at a time.

Use the marbles you can see to make a smart guess about all the marbles you cannot see.

  1. Watch How to Play to learn how to read a scoop.
  2. Shake, think, and lock in your guess.
  3. Earn 40 stars to unlock the Prize Vault.

My badges

0 of 40 stars earned

Teacher note

This game builds sampling and inference: using a small sample to make a careful guess about a whole group, and seeing that bigger samples give steadier guesses. It also takes proportional thinking, such as "12 out of 20 is like 60 out of 100."

Each jar allows one locked guess, scored by how close it is. On a 100 marble jar, a miss of 4 or less earns 3 stars, 9 or less earns 2, and 15 or less earns 1. A guess that is far off earns nothing and a new jar arrives, so guessing without thinking is slow. Scoops are random, so even careful students will sometimes miss. That is part of the lesson and makes a good class talk.

Students need 40 stars across four levels to unlock the prize video. When the video ends, all progress resets to zero. Progress is saved in the browser on that one Chromebook only. No supplies are needed.