Coins
There are nine coins. Eight coins are identical and the remaining coin weighs slightly less. By using a balance scale to compare coins (or groups of coins), how can you find the lighter coin with just two attempts at weighing?
In your response, try to explain your thinking as you describe the process you would use to determine which coin weighs slightly less than the others. Outlining your procedural thinking is a way of structuring mathematical proofs. Go step-by-step, considering all of the different factors at play.
Communicating your thoughts in math can be a challenge, but it is a very important skill to develop. You can use diagrams or tables to help explain your reasoning.
Tip: If you are having a hard time visualizing this task and you need manipulatives to work with, ask your teacher if your school has access to a scale in the math and science department. Use two unit blocks for the eight coins of the same weight and a single unit block for the coin of lighter weight.