Coin Problem

The goal of this problem is to use the balance scale to compare coin weights in order to discover which of the coins is counterfeit. After familiarizing yourself with the problem, see if you can discover the conterfeit coin in as few weighings as possible.

Using this virtual manipulative you may:

Compare coin weights

  1. Click and drag a coin to the left or right tray of the scale.
  2. Initially the balance is locked into place, so it will not tip when you put coins on it.

  3. Repeat the process until you have put the coins on the scale that you want to compare.
  4. Click the Weigh Coins button.
  5. The balance will be unlocked. The side of the scale with the heavier weight will go down.

Indicate that a coin is counterfeit

When you think you know which coin is counterfeit, place it on the Bad shelf to the left of the scale. A message will be displayed telling you if you are correct.

Choose a different type of problem

Initially, the virtual manipulative poses an eight coin problem. You may also choose to work a nine or twelve coin problem. To do so, click the button for the option you wish. The workspace will be initialized with the specified type of problem.

Obtain a new set of coins

After solving a problem you may choose to try it again. Click the New Coin Set button. A new set of coins will be presented and the weighings count will be reset to zero.