How to Become a Lightning Calculator

Part 1

Transcriber’s Notes:

Text enclosed by underscores is in italics (italics).

The whole number part of a mixed fraction is separated from the fractional part with -, for example, 2-1/2.

Additional Transcriber’s Notes are at the end.

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Multum in Parvo Library.

Vol. I. FEBRUARY, 1894. Published Monthly. No. 2.

How to Become a LIGHTNING CALCULATOR.

Smallest Magazine in the World. Subscription price, 50 cts. per year. Single copies, 5 cents each.

PUBLISHED BY A. B. COURTNEY, 671 Tremont Street, Boston.

Entered at Post-Office as second-class matter.

Instantaneous Addition.

Accuracy should be first considered, then rapidity. Quick adders, by the way, are the most accurate. Write the numbers in vertical lines, avoiding irregularity. This is important. Keep your thought on results not numbers themselves. Do not reckon 7 and 4 are 11 and 8 are 19, but say 7, 11, 19 and so on.

When the same number is repeated several times, multiply instead of adding.

When adding horizontally begin at the left.

3132 2453 12 | 6471 20 | 7312 15 | 2134 21 | ----- ---+ 21502

In adding long columns, prove the work, by adding each column separately in the opposite direction, before adding the next column. Many accountants put down both figures as in the illustration. The sum of the first column is 12; carrying one, the sum of the second is 20; carrying two, the sum of the third column is 15; carrying one, the sum of the fourth column is 21, and the total, 21502, is found by calling off the last two figures and the right-hand figures, following the wave line in the illustration. This method is better than the old one of penciling down the number to carry. If one desires to go back and add a certain column a second time, the number to carry is at hand and the former total is known.

How to Add Two Columns at Once.

2312 3253 2610 1256 3199 ----- 12630

To the inexperienced it will be a difficult task to add two columns at once, but many of those who have daily practice in addition find it about as easy to add two columns as one. Say 99 and 50 are 149, and 6 are 155, and 10 and 50 are 215 and 3 are 218, and 12 are 230. Carry 2, and say 33 and 12 are 45, and 20 are 65, and 6 are 71, and 30 are 101, and 2 are 103, and 23 are 126.

Much of the information here contained is compiled from W. D. Rowland’s valuable little volume, entitled “How to become expert with figures.” You can get this handy book by sending 25 cents in stamps to AMERICAN NATION CO., Boston.

Multiplication.

To Multiply Any Number by 11.

Write the first right-hand figure, add the first and second, the second and third, and so on; then write the left-hand figure. Carry when necessary.

219434 × 11 = 2413774

Put down the right-hand figure 4. Then say, 4 and 3 are 7; then, 3 and 4 are 7; then, 4 and 9 are 13, put down 3 and carry 1; then, 9 and 1 and 1 are 11, put down the 1 and carry 1; then, 1 and 2 and 1 are 4; then write the left-hand figure 2. In multiplying small numbers, such as 24 by 11, write the sum of the two figures between the two figures, making 264, the required product.

To Multiply by 101, 1001, etc.

To multiply by 101, add two ciphers to the multiplicand, and add to this the multiplicand.

Part 2

2341 × 101 = 234100 + 2341

To multiply by 1001, add three ciphers to the multiplicand, and add to this the multiplicand.

To Multiply by 5, 25, 125.

To multiply by 5, add a cipher and divide by 2.

To multiply by 25, add two ciphers and divide by 4.

To multiply by 125, add three ciphers and divide by 8.

Another Easy Way to Multiply.

82 54 ---- 4428

To multiply two figures by two figures, proceed as follows: Multiply units by units for the first figure.

Carry and multiply tens by units and units by tens, (adding) for the second figure. Carry and multiply tens by tens for the remaining figure or figures. In this example proceed as follows:

2 × 4 = 8 = 1st figure. (4 × 8) + (5 × 2) = 42. Therefore 2 = 2d figure. (5 × 8) + 4 carried = 44 = 3d and 4th figures.

By a little practice any one may become as familiar with this rule and as ready in its application as with the ordinary method.

To multiply any number by 2-1/2, add one cipher, and divide by 4.

To multiply any number by 3-1/3, add one cipher, and divide by 3.

To multiply by 33-1/3, add two ciphers, and divide by 3.

To multiply any number by 1-3/7, add one cipher, and divide by 7.

To multiply by 16-2/3, add two ciphers, and divide by 6.

To multiply by 14-2/7, add two ciphers, and divide by 7.

To multiply by 875, add three ciphers, and divide by 8.

To divide by 25, multiply by 4, and cut off two figures.

To divide by 125, multiply by 8, and cut off three figures.

To multiply by 12-1/2, add two ciphers, and divide by 8.

To find the value of any number of articles at 75 cents each, deduct one-quarter of the number from itself and call the remainder dollars.

To Subtract Any Number Consisting of Two Figures from 100.

Take the first figure from 9, and the second from 10. For example: in subtracting 73 from 100, or in taking 73 cents change out of a dollar, say 7 from 9 and 2, and 3 from 10 and 7, or 27 cents. Practice this rule. It is simple, and will be found particularly helpful in making change.

Divisions.

A number is divisible by 2 when the last digit is even.

A number is divisible by 4 when the last two digits are divisible by 4.

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.

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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.

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