ABACUS: MYSTERY OF THE BEAD
The Bead Unbaffled - An Abacus Manual
Alternative Example: 2.6 x 0.017 x 1.4 = 0.06188
There are plenty of instruments that don't have unit rods marked onto the beam. Also, it may be that some would prefer an alternative to having to predetermine the unit rod. The following is one solution for solving the question, "Where will the first decimal number be?"
The solution:
1) Count all the decimal numbers to be multiplied. (In the example above there are a total of 5 decimal numbers).
2) Place a 5 bead onto the soroban as a reminder of the 5 decimal numbers.
3) Simplify and solve the problem: 26 x 17 x 14 = 6188
4) From the right hand most number in the product count 5 places to the left. Set the decimal there.
This yeilds the correct answer, 2.6 x 0.017 x 1.4 = 0.06188
The problem could be set up this way
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1) Set 26 on rods MN
2) Set 16 (17-1) on rods GH
3) Set 13 (14-1) on rods DE
4) As a reminder, set 5 (the total decimal numbers) on rod A .
5) Solve the problem using the method shown on the main page.
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When the multiplication is complete we're left with 6188 on rods KLMN. The 5 bead on rod A reminds us we have 5 decimal numbers to consider. Count 5 rods to the left from rod N. This takes us to rod I making it the unit rod. The answer reads 0.06188 |
This might be the way to go if one were in a situation where multiplication problems were being given verbally. Just keep a running total of the decimal numbers, do the math and make the necessary decimal adjustments at the end.
back to Multifactorial Multiplication
June, 2005
Fernando Tejón
Totton Heffelfinger