2 ten-thous. 1 thous. 6 hund. 4 tens, and 6 units, which is 21646.
44. From this we deduce the following rules for subtraction:
I. Write the number which is to be subtracted (which is, of course, the lesser of the two, and is called the subtrahend) under the other, so that its units shall fall under the units of the other, and so on.
II. Subtract each figure of the lower line from the one above it, if that can be done. Where that cannot be done, add ten to the upper figure, and then subtract the lower figure; but recollect in this case always to increase the next figure in the lower line by 1, before you begin to subtract it from the upper one.
45. If there should not be as many figures in the lower line as in the upper one, proceed as if there were as many ciphers at the beginning of the lower line as will make the number of figures equal. You do not alter a number by placing ciphers at the beginning of it. For example, 00818 is the same number as 818, for it means
0 ten-thous. 0 thous. 8 hunds. 1 ten and 8 units;
the first two signs are nothing, and the rest is
8 hundreds, 1 ten, and 8 units, or 818.
The second does not differ from the first, except in its being said that there are no thousands and no tens of thousands in the number, which may be known without their being mentioned at all. You may ask, perhaps, why this does not apply to a cipher placed in the middle of a number, or at the right of it, as, for example, in 28007 and 39700? But you must recollect, that if it were not for the two ciphers in the first, the 8 would be taken for 8 tens, instead of 8 thousands; and if it were not for the ciphers in the second, the 7 would be taken for 7 units, instead of 7 hundreds.
46. EXAMPLE.