The abacus was created to aid in addition, subtraction, multiplication, and division in a time when pen and paper were not readily available to everyone. This tool enables its user to quickly and easily solve math problems even when dealing with very large numbers. In this investigation you will make an abacus and explore how to use it to solve math problems.
8 thin skewers (if yours are longer you can cut them down)
4 popsicle sticks
wood glue or hot glue gun
72 plastic beads (different colours, if possible)
pencil
Here are instructions to build one type of abacus. Of course, there are many other kinds as well. Use these instructions or do some research to find and explore other types.
Optional: Write in the place value of each row.
To add two numbers together, add each of the place values separately, starting from the right. For example, to add 25 to 125, we begin by moving up 5 beads in the row farthest to the right. We are one bead short, so we need to move all the beads down and exchange them for moving one bead up in the tens column. Next, move to the tens column. We move two beads up since 25 has 2 in the tens place. Once we have finished moving the beads, we count the new number of beads at the top and this is our new number.
This is done in very much the same way. If we wanted to subtract 20 from 125 we would begin with 125 on the abacus. Next, we start at the far right. We don't move any beads, because we have a 0 in the units place of our number, 20. Moving left to the tens place, we move two beads down, since 20 has a 2 in the tens place. Now we count the new number of beads at the top and this the answer.
Try doing some addition and subtraction with your abacus. Pay attention to the similarities it has to other addition and subtraction strategies you have used. Start with these problems, or make up and answer your own.
Use a range of additive and simple multiplicative strategies with whole numbers, fractions, decimals, and percentages.
Record and interpret additive and simple multiplicative strategies, using words, diagrams, and symbols, with an understanding of equality