2. What is the interest of $120.60 for one year and three months, at 6 per cent. per annum? Ans. $9.04c. 5m. 3. What is the interest on $187.061 for 10 months, at 6 per cent per annum? Ans. $9.85c 3m. 4. What is the interest and amount of 640 dollars for 4 years and 7 months, at 5 per cent. per annum? Ans. $146.66% interest. Am't. $786,663. 5. What is the interest of $300 for 4 years, 4 months, and 20 days, at 81 per cent. per annum? Ans. $111.914. 6. What is the interest of $5420 for 17 months, at 4 per cent per annum? Ans. $307.131. 7. What is the interest of $7200 for 14 months, at 6| per cent. per annum? Ans. $504. 8. What is the interest of $8050.87 for 3 years and 11 months, at 6 per cent. per annum? 8 Ans. $1891.95c, 5m. 9. What is the interest of $948.621 for 8 months, at per cent. per annum? Ans. $50.59c. 3m. 10. What is the interest of £421. 16s. 9d. for 2 years and 8 months, at 5 per cent. per annum? 2 Ans. £56. 4s. 103d. 11. What is the interest of 580 pounds for 5 years, months and 10 days, at 7 per cent per annum? Ans. £210.17s. 101d 12. What is the interest of $36 for 1 month, at 8 per cent. per annum? Ans. 24 cents. When the rate is 6 per cent. another method of finding the interest for any number of months, is, to multiply the principal by half the number of months and divide the product by 100 (or cut off the two right hand figures as before.) EXAMPLES. 1. What is the interest of $1500 for 4 months? 2. What is the interest of $7656 for 3 years and 4 months? $7656 20 half the number of months. 3. What is the interest of $230.25 for 8 months? Ans. $9.21. 4. What is the interest of $750 for 9 months? Ans. $33.75. 5. What is the interest of $967.64 for 28 months? Ans. $135.47. The interest for any number of days, at 6 per cent. can be found by multiplying the dollars by the number of days, and dividing the product by 60: the answer will be in cents. If the principal consist of dollars and cents, cut off the two right hand figures. Bank interest is reckoned by this rule.. 1. What is the interest of $1542 for 90 days? And of $754,54 for 60 days? $1542 610)1387810 2313 Ans. $23.13. $754.54 60 6|0)45272410 754 54 Ans. $7.54. 2. What is the interest of $3084 for 30 days at 6 per Ans. $15.42. cent. per annum? 3. What is the interest of $2324 for 54 days, at 6 per cent. per annum? Ans. $20.91. 4. What is the interest of $281.75 for 93 days, at 61 per cent, per annum? Ans. $4.36. CASE III. The amount, time, and rate per cent, given to find the principal RULE. Find the amount of 100 dollars at the rate and time given; then say, as the amount of 100 dollars, is to the amount given, so are 100 dollars to the principal required.. EXAMPLES. 1. What principal at interest for two years, at 6 per cent. per annum, will amount to $134.40? $100 6.00 2 12.00 100.00 $112 amount of 100 for two years. dolls. $ cts. dolls. dolls. Then, as 112: 134.40: 100 - 120 Ans. 2. What principal at interest for 5 cent. will amount to $780? years, 3. What principal at interest for 4 years and 3 months, at 6 per cent, will amount to $1192.25? Ans. $950. CASE IV. To find the rate per cent, when the amount, time and principal are given. RULE. Take the principal from the amount, the remainder will be the interest for the given time; then, as the principal is to one hundred dollars, so is the interest of the principal for the given time, to the interest of 100 dollars for the same time. Divide the interest of 100 dollars! thus found, by the time, and the quotient will be the rate per cent. EXAMPLES. 1. At what rate per cent, will $500 amount to $650 in three years? D. As 500 D. 650 Amount. 500 Principal. 100 :: 150. 30 Interest of 100. Then divide by the time 3)30(10 Ans. per cent. 30 2. At what rate per cent. per annum will $1850 double in 5 years? Ans. 20 per cent. 3. At what rate per cent. per annum, will 600 dollars amount to $856.50 in 9 years and 6 months? Ans. 41 per cent. CASE V. To find the time when the principal, amount, and rate per cent. are given. RULE. Find the interest of the principal for one year; find the interest of the principal for the whole time, by subtracting the principal from the amount; then divide the whole interest by the interest for one year-the quotient will show the time required. EXAMPLES. 1. In what time will $800 amount to $1000 at 5 per cent. per annum? 800 5 1000 Then, 4/0)2010 5 $40,00 200 Whole In't. Ans. 5 years. 2. In what time will $80 amount to $182.40 at 8 per cent. per annum? Ans. 16 years. 3. In what time will $600 amount to $798 at 6 per cent. yer annum? Ans. 51 years. COMPOUND INTEREST. Compound Interest is that which arises from the interest being added to the principal, and becoming a part of the principal, at each time of payment. RULE. Find the amount of the principal, for the time of the first payment, by Simple Interest; this amount, containing the principal and interest for the first year, will be the principal for the second year; and the amount of this principal, which consists of the principal and interest for the second year, will be the principal for the third year, and so on, for any number of years. From the last amount, subtract the given principal, and the remainder will be the compound interest. EXAMPLES. 1. What is the compound interest of $8000 for two years, at 6 per cent per annum? $8000 Interest for the first year 480|00 Amount 8480 6 In't. for the second year 508.180 Principal 8480,00 8988.80 Subtract 8000.00 $988.80c. Answer. 2. What is the compound interest of $554 for 3 years, at 8 per cent. per annum? Ans. $143.88. 3. What is the compound interest of $744 for 2 years, Ans. $107.80c. 5m at 7 percent. per annum? 4. What is the compound interest of $50 for 8 years, at 8 per cent. per annum? Ans. $42.54c. 6m 5. What is the compound interest of £48. 5s. for 3 years, at 6 per cent. per annum? Ans. £9. 4s. 31d. In computing Interest on Notes. When a settlement is made within a short time from the date or commencement of interest, it is generally the custom to proceed according to the following RULE. Find the amount of the principal, from the time the interest commenced to the time of settlement, and likewise the amount of each payment, from the time it was paid to the time of settlement; then deduct the amount of the several payments from the amount of the principal. Exercises for the Slate. 1. For value received, I promise to pay Rufus Stanly, or order, Three Hundred Dollars, with interest. April 1, 1825. $300. PETER MOSELY. |