To find the accurate interest on any sum of money at a given rate for one year, multiply the sum by the rate and divide by 100.
To find the accurate interest on any sum of money at a given rate for any given number of days, multiply the interest for one year by the number of days and divide the product by 365.
Equation of Payments.
Equation of Payments is the process of finding when two or more sums due at different times may be paid at once, without loss to debtor or creditor. The time for such payment is called the equated time.
To equate two or more payments, multiply each payment by its time, and divide the sum of the products by the sum of the payments.
The times of the several payments must be in the same denomination, and this will be the denomination of the answer.
Less than 1/2 day is rejected; 1/2 day or more counts as 1 day. If the date is required, reckon the equated time forward from the given date.
The Lightning Calculator’s Addition.
| 4379321 |
| 5620679 |
| 2184509 |
| 7815491 |
| 2105610 |
| 3453173 |
| 25558783 |
There are experts who can add very rapidly. The best of them, however, cannot add up a column of ones any faster than you can. Here is how some of the rapid addition is performed. The operator writes a line of figures, then another, and so on. The second line, however, added to the first makes nines, except at the extreme right, where the two figures add to ten. The third and fourth bear the same relation, and as many more as he chooses to put down. The last two lines, however, are put down at random. Now, to add these columns, he begins anywhere, perhaps at the left-hand side, putting down 2 (the number of pairs above), then by simply adding the two bottom lines, he gets the correct sum.