* On this statement is founded one of the practical rules for computing interest, as will be hereafter shown. 3. CONJOINED PROPORTION. CONJOINED PROPORTION is when the coins, weights, or measures of several countries are compared in the same sum. Case I. To find how many of the last kind of coin, weight, or measure, mentioned in the question, are equal to a given number of the first. RULE.* Make the given number the third term. Of the other numbers, multiply all the antecedents together for the first term, and all the consequents together for the second; then state the question, and proceed as in the Single Rule of Three. * This and the following rule may often be abridged by cancelling where the same number is found among the antecedents and consequents. The proof is by several statements in the Single Rule of Three. Case II. To find how many of the first kind of coin, weight, or measure, mentioned in the question, are equal to a given number of the last. RULE.-Proceed as in the first case, only make the product of the consequents the first term, and that of the antecedents the second. Examples. 1. If 100lb. in America make 2. If 6 braces at Leghorn make 95lb. Flemish, and 19lb. Flemish | 3 ells English, and 5 ells Eng25lb. at Bolognia, how many glish 9 braces at Venice, how pounds in America are equal to many braces at Leghorn will 50lb. at Bolognia ? make 45 braces at Venice ? Ans. 50 braces. lb. lb. Ant. Con. lb. 95 2375: 1900 :: 50 1900 475 190 2375 50 3. If 20lb. at Boston make 23 at Antwerp, and 155lb. at Antwerp make 180 at Leghorn; how many pounds at Boston are equal to 144 at Leghorn ?. Ans. 107 lb. QUESTIONS. 1. By what other name is the Dou- 2. What does this rule teach? 4. In stating the question, how are 5. What is to be done with the other two terms? 6. If the blank fall under the third term, how do you proceed? 7. How, if it fall under the first qr second term? 8. What is Conjoined Proportion? 9. How do you proceed, when it is 10. required to find how many of SECTION V. Interest. INTEREST is a premium allowed for the use of money. It is computed at so many dollars a year for the use of each hundred dollars, called so much per cent. per annum.. The principal is the sum which is upon interest. The rate is the per cent. per annum agreed on. 1. SIMPLE INTEREST. Simple Interest is that which is allowed for the principal only. Case I. To find the interest on any sum in Federal or English money. Rule.† 1. Multiply the principal by the rate, and divide the product by 100, the quotient will be the interest for one year. 2. Multiply the interest thus found, by the number of the product will be the interest for that time. years, and 3. If there be months and days, for the former take proportional parts of the interest for one year, and for the latter, proportional parts of the interest for one month, allowing 30 days to a month. *The rate is generally established by law. Six per cent. is the legal interest in the several New-England States, and this is to be understood in this work, where the rate is not mentioned. In New-York, legal interest is 7 per cent. As + This rule is barely an application of the Single Rule of Three, or saying as 100, or £100, is to the rate, so is the principal to the interest for one year. EXAMPLE.--What is the interest of $250 for one year, at 6 per cent? $100 6:250: Ans. $15. The reason for the remaining part of the rule must be obvious. When the months are not an aliquot part of a year, divide them into two such parts as shall be aliquot parts of a year, find the interest of those two, and add them together. The same may be done when the days are not an aliquot part of a month. |