The trouble is that when the poor fellow came to multiply by the
“naught” he forgot in the first instance that it was nothing, and
that the biggest number in the world multiplied by nothing will
produce nothing. He knew that something ought to go down there, and
so in sheer desperation he wrote down the number he was multiplying.
In the second instance, while he recognized that nothing is
nothing, he forgot that all our figuring is done by columns, as we
saw in our last lesson; so that when we are multiplying by tens we
must put our first figure down in the hundreds column, and so on.
By forgetting this he multiplied his number by two hundreds, but
put his first figure down in the tens columns, and thus he really
multiplied by only 28 instead of 208.
Now, the very simplest way to avoid this sort of mistake is to “go
through the motions” of multiplying by the “naught” or “zero.” Thus:
The Right Way. 3,125
208
------
25000
0000
6250
-------
650,000
This looks a little clumsy, perhaps, but it is the logical way--to
go through the process of saying naught times 5 is naught, naught
times 2 is naught, etc., putting down the results in the proper
columns. It is the safest way, if you are the least bit weak on the
principles of numbers, to do even the process of multiplying by
whole hundreds. Thus:
3,125
200
------
0000
0000
6250
-------
625,000
By writing his example in the “short cut” style I have seen many a
man make this mistake:
Wrong. 3,125
200
-----
62500
That is, after setting down his two surplus ciphers, when he
obtained another in multiplying 5 by 2, he forgot that it was a
new one and went right on to the next process. If you are in that
position that you must really learn your arithmetic all over again,
stick to the logical method of showing every process and learn the
“short cuts” afterward.
Now, when the reverse situation arises in division, a similar error
is of frequent occurrence. Suppose we are to divide 650,000 by
3,125. This sometimes results:
The Wrong Way. 3,125)650,000(28
625 0
-----
25,000
25,000
That is, the figurer, when he came to try to divide 2,500 by 3,125,
realizing that it would not “go,” simply “brought down” another
figure. He forgot that the real mental process was 3,125 goes
into 2,500 no times, or produces “naught,” and that “naught,” or
“cipher,” must be set down in the proper tens column. The only safe
way, again, is to indicate every process; to “bring down” but one
figure at a time and to set down every result, even the “nothings,”
in its proper place. That will make our example look like this:
Public-domain text, read in full here on John Shaqi.
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