Part 3

To divide by 12-1/2, multiply by 8, and cut off two figures.

Simple Discount Rule.

This simple rule is in use in many houses where several discounts are allowed from list prices. Suppose the list price of a piano to be $500, and you allow an agent 25, 20 and 10 off.

100 100 100 25 20 10 --- --- --- 75 × 80 × 90 = .540000

Subtract each from 100 and multiply and you get .54. $500 × .54 = $270, the agent’s price.

* * * * *

If you want to get a complete book on quick calculating, comprising all modern methods, together with a vast amount of other valuable matter, pertaining to business, send 25 cents to AMERICAN NATION CO., Boston, Mass., for a volume of “How to Become Expert at Figures.”

Percentage.

The name percentage is applied to certain arithmetical exercises in which 100 is used as the basis of computation. Per cent. is an abbreviation of the Latin per centum, meaning by the hundred. This sign % is used for the words per cent. Thus, 10% of a number equals 10/100, or 1/10 of the number; 50% equals 50/100, or 1/2, etc.

FRACTIONAL EQUIVALENTS.

50 % = .50 = 1/2. 33-1/3 % = .33-1/3 = 1/3. 25 % = .25 = 1/4. 20 % = .20 = 1/5. 16-2/3 % = .16-2/3 = 1/6. 12-1/2 % = .12-1/2 = 1/8. 10 % = .10 = 1/10. 8-1/3 % = .08-1/3 = 1/12. 6-1/4 % = .06-1/4 = 1/16. 5 % = .05 = 1/20. 2-1/2 % = .02-1/2 = 1/40.

Accurate Interest.

Interest is the sum charged for the use of money. It is really the use of money or the benefit derived from its use. The principal is the sum for the use of which interest is paid. The rate of interest is the per cent. of the principal charged for its use for one year. Simple interest is the interest on the principal only, for the full time; compound interest is interest on the principal for the full time, and interest on each interest payment after it becomes due.

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.

Bank Discount.

The sum charged by a bank for cashing a note or time draft is called bank discount. This discount is the simple interest, paid in advance, for the number of days the note has to run. Wholesale business houses usually sell goods on time and take notes from the retailers in payment. These notes are not often for a longer period than three months. Some are placed in the banks for collection, others are discounted. When a note is discounted at a bank the payee endorses it, making it payable to the bank. Both maker and payee are then responsible to the bank for its payment. If the note is drawing interest the discount is reckoned on and deducted from the amount due at maturity. Most notes discounted at banks do not draw interest. The time in bank discount is always the number of days from the date of discounting to the date of maturity.

Example. A note of $250, dated July 7th, payable in 60 days, is discounted July 7th, at 6 per cent.; find the proceeds.

This note is due in 63 days, or September 8th. The accurate interest of $250 for 63 days at 6 per cent. is $2.59. The proceeds, then, will be $250 - $2.59, or $247.41.

How to Make Change.