EXAMPLES. 1. What is the interest of $573.15 for 5 years at 6 per cent. ? OPERATION. $573.15 the principal. 0.06 rate per cent. $34.3890 one year's interest. 5 number of years. Ans. $171.945-five years' interest. 2. What is the interest of $600 for 4 years at 5 pcr cent.? Ans. $120. 3. What is the interest of $725 for 8 years at 4 per cent.? Ans. $261. 4. What is the interest of $149 for 5 years at 2 per cent.? Ans. $14.90. 5. What is the interest of $225.25 for 10 years at 4 per cent. ? Ans. $90.10. 6. What is the interest of $311.30 for 11 years at 10 per cent. ? Ans. $342 43. 7. What is the interest of $501.50 for 2 years at 31 per cent. ? Ans. $35.105. CASE II. To find the interest on any given principal, for any given time, at any given rate per cent. Suppose we wish the interest of $126 for 3 years 5 months and 15 days, at 7 per cent. 1 mo. of 4 mos. 735 = 1 15 dys.=of 1 mo. 3675=15 days' Ans. $30-5025=3 yrs. 5 mos. and 15 days' int. Hence the following RULE. Multiply the principal by the rate per cent. expressed in decimals; the product will give one year's interest, which, multiplied by the number of years, will give the interest for the tine expressed in years. Then find the interest for the months and days by means of aliquot parts, as in Practice. EXAMPLES. 1. What is the interest of $39-42 for 1 year, 5 months, and 11 days, at 7 per cent.? NOTE. We have not extended our work to more than three places of decimals, but have added 1 to the third place whenever the fourth decimal figure would be 5 or greater. 2. What is the interest of $47.13 for 7 months and 21 days, at 7 per cent. ? Ans. 2.118. 3. What is the interest of $321.21 for 3 months and 15 days, at 6 per cent.? Ans. $5.621. 4. What is the interest of $270 for 2 months and 8 days, at 7 per cent. ? Ans. $3.57. 5. What is the interest of $404-44 for 1 year, 5 months and 4 days, at 7 per cent.? Ans. $40-422. 6. What is the interest of $99.99 for 11 months and 29 days, at 5 per cent. ? Ans. $4.986. 7. What is the interest of $37.50 for 6 months and 10 days, at 6 per cent.? Ans. $1.287. 8. What is the interest of $49.49 for 8 months and 8 days, at 7 per cent. ? CASE III. Ans. $2.386. To find the interest on any given principal for any given time at 6 per cent.? The interest on $100 for one year, at 6 per cent., being $6, it follows that the interest on $1, for one year, is $0.06; and since 2 months is of a year, the interest on $1, for two months, is $0.01; again, since 6 days is of 2 months, when we reckon 30 days to each month, it follows that the interest on $1, for 6 days, is 80-001. Hence, if we call half the number of months, CENTS, and one-sixth the number of days, MILLS, we shall obtain the interest of $1 for the given time, at 6 per cent. The interest of $1 being multiplied by the number of dollars in the given principal, will obviously give the in terest sought. As an example, suppose we wish the interest of $125 for 1 year, 5 months and 18 days, at 6 per cent. $0.085=int. of $1 for 1 y. 5 m.=17 months. 66 66 18 days. 3= 66 $0.088 int. of $1 for 1 y. 5 m. and 18 days. If now we multiply $0.088 by 125, the number of dollars in the principal; or, which is the same thing, if we multiply $125 by 0-088, we shall find $125 × 0.088=$11, for the interest sought. Hence we have this RULE. 1. Call half the number of months, CENTS; one-sixth the number of days, MILLS; and the result will be the interest of $1 for the given time. II. Multiply the interest of $1, thus found, by the number of dollars in the given principal, and the product being pointed off by the rule for decimals, will give the interest required. EXAMPLES.. 1. What is the interest of $49.37, for 13 months and 15 days, at 6 per cent.? In this example, we find the interest on $1, for 13 months and 15 days, at 6 per cent., to be $0.0675, which, multiplied by 49-37, the number of dollars in the principal, gives $3.332475, for the interest on $49-37, for the given time. 2. What is the interest of $608-62, for 1 year and 9 months, at 6 per cent.? Ans. $63.9051. 3. What is the interest of $341.13, for 7 years and 9 days, at 6 per cent. ? Ans. $143.786295. 4. What is the interest of $100, for 16 years and 8 months, at 6 per cent.? Ans. $100. 5. What is the interest of $591.03, for 4 years, 3 months Ans. $151 402185. and 7 days, at 6 per cent.? 6. What is the interest of $0.134, for 4 months and 3 days, at 6 per cent. ? Ans. $0.002747. 7. What is the interest of $7.50, for 7 months, at 6 per cent. ? Ans. $0.2625. 8. What is the interest of $371-01, for 4 years and 15 days, at 6 per cent.? Ans. $89.969925. 9. What is the interest of $57.92, for 3 and 9 days, at 6 per cent.? years, 7 months Ans. $12.53968. 10. What is the interest of $329, for 5 years and 13 days, at 6 per cent. ? Ans. $99 4125. 11. What is the interest of $47-39, for 1 year and 7 months, at 6 per cent. ? Ans. $4.50205. CASE IV. To find the interest on any given principal, for any given time, at any given rate per cent. Interest at 6 per cent. increased by viously give the interest at 7 per cent. of itself will ob The interest at 6 per cent. increased by of itself will give the interest at 8 per cent. If we diminish the interest at 6 per cent. by of itself, we shall obtain the interest at 5 per cent. And in all cases, by increasing or decreasing the interest at 6 per cent., in the proper ratio, we may obtain the interest at any other desired rate. As an example, suppose we wish the interest of $300 for 1 year, 3 months, and 12 days, at 4 per cent. By Case III. we readily find the interest of $300 for 1 year, 3 months and 12 days, at 6 per cent., to be $23.10 |