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