13. What is the interest of $144 for 1 year 8 months at 5%? 14. What is the interest of $556 for 3 years 5 months 7 days at 8%? 15. What is the interest of $720 at 5% for 1 y. 7 mo. 18 d.? $720 12) $36.00 $3.00 19.6. $58.80 Solution. One year's interest is .05 of $720, or $36; the interest for 1 y. 7 mo. 18 d., 19-6 19.6 or 19.6 mo., or 19 years, is 1× $36, or $58.80. In this example, 1 year's interest being a multiple of 12, we divide by the denominator of the multiplier before multiplying by the numerator. 16. Find the amount of $1500 for 2 y. 6 mo. 15 d. at 6%. 260. General Rule for Interest. Multiply the principal by the rate, and this product by the time in years. To find the amount, add the principal and the interest. Let p represent the principal, r the rate per cent, i the interest, t the time, and a the amount, and we have the FORMULAS. i=pxrxt. a = p + i. NOTE. In interest partial results may be carried to four places of decimals. The answers, in business transactions, are deemed sufficiently exact if the mills are omitted, and when they are five or more, the cents are increased by 1. 17. What is the interest of $2464 for 2 y. 9 mo. 15 d. at 5%? 18. What is the interest of $2503.75 for 3 y. 10 mo. 21 d. at 6%? 19. What is the interest of $ 560.50 for 4 y. 10 d. at 7 % ? 20. What is the interest of $ 97.16 for 1 y. 5 mo. at 6% ? 21. What is the interest of $156.80 for 3 y. 1 mo. 3 d. at 4%? 22. What is the interest of $865 for 1 y. 9 mo. 24 d. at 8%? 23. What is the interest of $ 890 for 5 y. 7 mo. 8 d. at 6%? 24. What is the amount of $5000 for 3 y. 11 mo. 10 d. at 7%? Six per cent Method. 261. The Interest of any sum, at 6 per cent a year, For 12 months, or 1 year, is .06 of the principal. For 2 months, or year, is .01 of the principal. For 1 month, or 30 days, is .00 of the principal. month, or 6 days, is .001 of the principal. month, or 1 day, is .000 of the principal. For For 262. Hence, as a convenient method of reckoning interest at 6 per cent, Or, Or, Multiply of .01 of the principal by the time in months. Multiply .001 of the principal by of the time in days. Of the principal take 6 times as many hundredths as years, as many hundredths as months, and as many thousandths as days. 25. What is the interest of $926 for 3 years 11 months 15 days at 6%? 26. What is the interest of $ 340 for 103 days at 6%? 27. What is the interest of $1650 for 2 y. 7 mo. 18 d. at given time is .158 of the principal, or .158 of $1650, or $ 260.70. 33. $85.90 for 3 y. 6 mo. 27 d. ? 34. $1992.25 for 93 days? 35. $15600 for 4 y. 7 mo. 19 d. ? 36. What is the amount of $1400 for 2 years 6 months? 37. What is the amount of $7000 for 5 years 3 months? 263. For any other rate than 6 per cent we may, when more convenient than to apply the general rule (Art. 260), Find the interest at 6 per cent, and increase or diminish this interest by such part of itself as will give the interest at the required rate. That is, to find 4% interest subtract from the 6% interest of itself; 41% interest, subtract from the 6% interest of itself; 5% interest, subtract from the 6% interest of itself; 7% interest, add to the 6% interest of itself; and so on 38. What is the interest of $ 545 for 8 mo. 24 d. at 4% ? 39. What is the interest of $78.50 for 123 days at 5%? 40. What is the interest of $64.70 for 2 y. 5 mo. at 7% ? 41. What is the interest of $ 1440 for 11 mo. 23 d. at 41%? 42. What is the interest of $9500 for 3 y. 6 mo. 17 d. at 7%? 43. What is the interest of $600.80 for 2 y. 11 mo. 3 d. at 8%? 44. What is the interest of $20000 for 63 days at 5%? 45. What is the interest of $340.90 for 4 y. 7 mo. 11 d. at 7%? 46. What is the interest of $ 15420 for 9 mo. 24 d. at 61% ? 47. What is the interest of $ 374.75 for 3 y. 9 mo. at 8%? 48. Ernest Williams borrowed, April 5, 1881, $525 at 7% interest, and kept it until May 16, 1882. What was the amount? 49. A note for $450.60, dated March 5, 1880, was paid Dec. 31, 1881, with interest at 7%. What was the amount? Short Method. 264. The following method of computing 6% interest is often very convenient, especially for short times. Find 60 days' interest by taking .01 of the principal. Then take such multiples or parts of this interest as the given time may require. 50. What is the interest of $2460 for 3 mo. 18 d. ? 51. What is the interest of $480 for 84 days at 71%? |
