at 4 per cent. Dr. 9. Required the interest on the following account current, up to Dec. 31, John Cole in account current with Richard Owen. Cr. £ £. II. TO FIND THE AMOUNT OF A GIVEN SUM AT A GIVEN RATE FOR A GIVEN TIME. Rule. Calculate the interest by the preceding Rule, and add to it the principal. 11. TO FIND THE TIME IN WHICH THE INTEREST ON A GIVEN Rule. Calculate the interest for 1 year, and find the ratio of the given interest to this; the result will be the number of years required. If the amount be given, instead of the interest, subtract the principal, thus obtaining the interest, and proceed as before. EXAMPLE. Find the time in which the interest on £750: 10:0 will amount to £712 19: 6 at 4 per cent. IV. TO FIND THE RATE PER CENT. AT WHICH THE INTEREST ON A GIVEN PRINCIPAL WILL AMOUNT TO A GIVEN SUM IN A GIVEN TIME. Rule. Calculate the interest for the given time at 1 per cent. and find the ratio of the given interest to this; the result will be the rate required. If the amount be given, instead of the interest, subtract the principal, so obtaining the interest, and proceed as before. EXAMPLE. Find at what rate per cent. £755 will amount to £1132: 10: 0 in 10 years. Int. at 1 per cent. = £7.55 X 10 £1132.5 Amount. £7 55 = Principal £377.5 Interest. = £75.5 V. TO FIND WHAT PRINCIPAL WILL AMOUNT TO A GIVEN SUM AT A GIVEN RATE IN A GIVEN TIME, OR TO FIND THE PRESENT WORTH OF A GIVEN SUM. Rule. Calculate the amount of £1 for the given time at the given rate, and find the ratio of the given amount to this; the result will be the principal required in pounds. If the interest be given, find the interest on £1, and proceed as before. EXAMPLE. Find what sum will amount to £1137: 10: 0 in 2 years at 5 per cent. = .1375£. Amount given..... Ans. £1000. 1.1375£. J. B.-Compound Interest. TO FIND THE AMOUNT OF A GIVEN PRINCIPAL AT A GIVEN RATE Rule. Find the amount of £1 for 1 term in decimals of £1; raise this to a power equal to the number of terms, and multiply the principal by the result. 11. TO FIND THE COMPOUND INTEREST ON A GIVEN PRINCIPAL. Rule. Find the amount (by preceding rule) and subtract the principal. EXAMPLE. Find the amount of £1066: 13: 4 for 3 years at 3 per cent. compound interest. A TO FIND THE PRINCIPAL, WHICH AT COMPOUND INTEREST FOR GIVEN NUMBER OF TERMS WILL AMOUNT TO A GIVEN SUM. Rule. Find the amount of £1 for 1 term in decimals of £1; raise this to a power equal to the number of terms; and divide the given amount by the result. If the interest be given instead of the amount, add the principal, so obtaining the amount, and proceed as before. EXAMPLE. What sum lent out at compound interest at the rate of 4 per cent. will amount to £2050 10 8 in 3 years? X. DISCOUNT. TO FIND THE TRUE DISCOUNT ON A DEBT DUE AT A GIVEN TIME. Rule 1. Find the present worth of the debt, and subtract it from the debt; the difference is the discount. Rule 2. Find the interest on the debt for the given time, and also the amount of £1 for the given time; the ratio of the former to the latter is the discount in pounds. EXAMPLES. 1. Find the discount on £845: 16: 4 due in 2 years, 8 months, at 44 per cent. per annum. |