The first item on the agenda is a new way to do basic multiplication: we shall multiply without using any memorized multiplication tables. Does this sound impossible? It is not only possible, it is easy.
A word of explanation, though: we are not saying that we disapprove of using tables. Most people know the tables pretty well;; in fact, perfectly, except for a few doubtful spots. Eight times seven, or six times nine are a little uncertain to many of us, but the smaller numbers like four times five are at the command of everyone> We approve of using this hard – won knowledge. What we intend to do now is consolidate it. Later in this chapter we shall come back to this point. Now we wish to do some multiplying with out using the multiplication tables.
Let us look at the case of multiplying by eleven. For the sake of convenience in explaining it, we first state the method in the form of rules:
MULTIPLICATION BY ELEVEN:
a)The last number of the multiplicand ( number multiplied) is put down as the right-hand figure of the answer.
b) Each successive number of the multiplicand is added to its neighbor at the right.
c) The first number of the multiplicand becomes the left-hand number of the answer. This is the last step.
In the Trachtenberg system you put down the answer one figure at a time, right to left, just as you do in the system you now use. Take an easy example, 633 times 11:
6 3 3 x 1 1 = The answer will appear under the 633,
one figure at a time, from right to left, as we apply the rules. This will be our form for setting up the work from now on. The asterisks above the multiplicand of our example will quickly identify the numbers being used in the each step of our calculation. Let us apply the rules:
First Rule : Put down the last figure of 633 as the right-hand figure of the answer: 6 3 3 x 1 1 = _ _ _ 3
Second Rule: Each successive figure of 633 is added to its right-hand neighbor.3 plus 3 is 6: 6 3 3 x 1 1 = _ _ _ 63
Apply the rule again, 6 plus 3 is 9: : 6 3 3 x 1 1 = _ _ _ 963
Third Rule: The first figure of 633, the 6, becomes the left-hand figure of the answer : 6 3 3 x 1 1 = _ __ 6963
The answer is : 6,963.