Subtraction Using an Abacus
Select a problem set using the buttons above, then use your mouse or
tab key to select a question. Fill in the blank with the correct answer.
Be sure to use commas every three places..
You can open the online abacus to help solve these problems.
You can move the abacus around by grabbing the red bar at the top.
When you have answered all of the questions, ask Charlie how you did.