HOW TO CALCULATE.
PRACTICAL RULES, SHORT METHODS, AND PROBLEMS USED IN BUSINESS COMPUTATIONS.
Rapidity and accuracy in making estimates and in figuring out the result of business transactions is of the greatest necessity to the man of business. A miscalculation may involve the loss of hundreds or thousands of dollars, in many cases, while a slow and tedious calculation involves loss of time and the advantage which should have been seized at the moment. It is proposed in the following pages to give a few brief methods and practical rules for performing calculations which occur in every-day transactions among men, presuming that a fair knowledge of the ordinary rules of arithmetic has previously been attained.
ADDITION.
To be able to add up long columns of figures rapidly and correctly is of great value to the merchant. This requires not only a knowledge of addition, but in order to have a correct result, one that can be relied upon, it requires concentration of the mind. Never allow other thoughts to be flitting through the mind, or any outside matter to disturb or draw it away from the figures, until the result is obtained. Write the tens to be carried each time in a smaller figure underneath the units, so that afterwards any column can be added over again without repeating the entire operation. By the practice of addition the eye and mind soon become accustomed to act rapidly, and this is the art of addition. Grouping figures together is a valuable aid in rapid addition, as we group letters into words in reading.
| 862 \ |
| 538 / |
| 674 \ |
| 843 / |
| ____ |
| 2917 |
Thus, in the above example, we do not say 3 and 4 are 7 and 8 are 15 and 2 are 17, but speak the sum of the couplet, thus 7 and 10 are 17, and in the second column, 12 and 9 are 21. This method of grouping the figures soon becomes easy and reduces the labor of addition about one-half, while those somewhat expert may group three or more figures, still more reducing the time and labor, and sometimes two or more columns may be added at once, by ready reckoners.
Another method is to group into tens when it can be conveniently done, and still another method in adding up long columns is to add from the bottom to the top, and whenever the numbers make even 10, 20, 30, 40 or 50, write with pencil a small figure opposite, 1, 2, 3, 4 or 5, and then proceed to add as units. The sum of these figures thus set out will be the number of tens to be carried to the next column.
| 62 | 2 | 8 | |
| 3 | 52 | 41 | |
| 2 | 8 | 4 | |
| 9 | 6 | 2 | |
| 72 | 1 | 82 | |
| 8 | 32 | 5 | |
| 5 | 2 | 7 | |
| 11 | 3 | 21 | |
| 5 | 8 | 8 | |
| _________________ | |||
| 5 | 0 | 2 | 8 |