215 AN APPENDIX, CONTAINING SHORT RULES, FOR CASTING INTEREST AND REBATE; TOGETHER WITH SOME I USEFUL RULES, FOR FINDING THE CONTENTS OF SUPERFICIES, SOLIDS, &c. SHORT RULES, FOR CASTING INTEREST AT SIX PER CENT. I. To find the interest of any sum of shillings for any number of days less than a month, at 6 per cent. RULE. 1. Multiply the shillings of the principal by the number of days, and that product by 2, and cut off three figures to the right hand, and all above three figures will be the interest in pence. 2. Multiply the figures cut off by 4, still striking off three figures to the right hand, and you will have the farthings, very nearly. EXAMPLES. 1. Required the interest of 5l. 8s. for 25 days. 5,8=108×25×2=5,400, and 400×4=1,600 Ans. 5d. 1,6grs. 2. What is the interest of 211. 3s. for 29 days P Ans, 2s, Od. 2grs, FEDERAL MONEY. II. To find the interest of any 'number of cents for number of days less than a month, at 6 per cent. RULE, any Multiply the cents by the number of days, divide the product by 6, and point off two figures to the right, and all the figures at the left hand of the dash, will be the interest in mills, nearly. EXAMPLES. Required the interest of 85 dollars, for 20 days. $ cts. 85-8500×20-6-283,33. mills. Ans. 283 which is 28cts. 3 mills. 2. What is the interest of 73 dollars 41 cents, or 7341 cents, for 27 days, at 6 per cent. ? Ans. 350 mills, or 33cts. III. When the principal is given in pounds, shillings, &c. New-England currency, to find the interest for any number of days, less than a month, in Federal Money. RULE. Multiply the shillings in the principal by the number of days, and divide the product by 36, the quotient will be the interest in mills, for the given time, nearly; omitting fractions. EXAMPLE. Required the interest, in Federal Money; of 271. 159. for 27 days, at 6 per cent. Ans. 27 15=555×27÷36=416mills.=41cts. 6m. IV. When the principal is given in Federal Money, and you want the interest in shillings, pence, &c. New-Engfand currency, for any number of days less than a month. RULE. Multiply the principal, in cents, by the number of days, and point off five figures to the right hand of the product, which will give the interest for the given time, in shillings and decimals of a shilling, very nearly. EXAMPLES. cts. S. A note for 65 dollars, 31 cents, has been on interest 25 days; how much is the interest thereof, in New-England currency? s. d. qrs. Ans. 65,31-6531×25-1,63275=1 72 REMARKS.-In the above, and likewise in the preceding practical Rules, (page 127) the interest is confined at six per cent. which admits of a variety of short methods of casting; and when the rate of interest is 7 per cent. as established in New-York, &c. you may first cast the interest at 6 per cent. and add thereto one sixth of itself, and the sum will be the interest at 7 per cent. which perhaps, many times, will be found more convenient than the general rule of casting interest. EXAMPLE. Required the interest of 75l. for 5 months at 7 per £. s. d. 37,5=1 17 6 for 5 months at 6 per cent. Ans. £2 39 for ditto at 7 per cent. A SHORT METHOD FOR FINDING THE REBATE OF ANY GIVEN SUM, FOR MONTHS AND DAYS. RULE. Diminish the interest of the given sum for the time by its own interest, and this gives the Rebate very nearly. EXAMPLES. 1. What is the rebate of 50 dollars for six months, at 6 per cent.? The interest of 50 dollars for 6 months, is $ cts. 1 50 4 Ans. Rebate, $1 46 2. What is the rebate of 150l. for 7 months, at 5 per cent.? £. s. d. Interest of 150l. for 7 months, is 4 7 6 261 Ans. £4 4 11 nearly. By the above Rule, those who use interest tables in their counting-houses, have only to deduct the interest of the interest, and the remainder is the discount. A concise Rule to reduce the currencies of the different States, where a dollar is an even number of shillings, to Federal Money. RULE I. Bring the given sum into a decimal expression by in spection, (as in Problem I. page 87) then divide the whole by ,3 in New-England and by ,4 in New-York currency, and the quotient will be dollars, cents, &c. EXAMPLES. 1. Reduce 54l. 8s. 31d. New-England currency, to Federal Money. ,3)54,415 decimally expressed. Ans. $181,38 cts. 2. Reduce 7s. 114d. New-England currency, to Federal Money. 7s. 114d.=£0,399 then,,3),$99 Ans. $1,33 3. Reduce 513l. 16s. 10d. New-York, &c. currency to Federal Money. ,4)513,842 decimal Ans. $1884,60 4. Reduce 19s. Jąd. New-York, &c. currency, to Federal Money. ,4)0,974 decimal of 19s. 5;d, $2,43 Ans. 5. Reduce 647. New-England currency, to Federal Money. ,3)64000 decimal expression. $213,334 Ans. NOTE. By the foregoing rule you may carry on the decimal to any degree of exactness; but in ordinary practice, the following Contraction may be useful. RULE II. To the shillings contained in the given sum, annex 8 times the given pence, increasing the product by 2; then divide the whole by the number of shillings contained in a dollar, and the quotient will be cents. EXAMPLES. 1. Reduce 45s. 6d. New-England currency, to Federal Money. 6x8+250 to be annexed, $ cts.* $7,58% Ans. 758 cents. 7,58 2. Reduce 21. 10s. 9d. New-York, &c. currency, to Federal Money. Then 8)5074 9x8+274 to be annexed. Or thus, 8)50,74 $ cts. Ans. 634 cents.=6 34 $6,34 Ans. N. B. When there are no pence in the given sum, you must annex two cyphers to the shillings; then divide as before, &c. 3. Reduce 31. 5s. New-England currency, to Federal money. 31. 5s.-65s. Then 6)6500 Ans. 1983 cents. |