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The amount, time and ratio given, to find the principal.
Rule.--Multiply the ratio by the time; add unity to the product for a divisor, by which fum divide the amount, and the quotient will be the principal.
Ε Χ Α Μ What principal will amount to £ 1045 145. in 7 years, at £6 per cent. per annum ?
Divisor=1,42) 1045,7(736,4084 +
(4 736 8s. 2d. What principal will amount to £ 3810 in 6 years, at £4 per cent. per annum ?
Anf. £3000. 3.
What principal will amount to £666 95. od. in 3 years, at £ 5 per cent. per annum?
Anf. £ 563.
3. The amount, principal and time given, to find the ratio.
Rule.--Subtract the principal from the amount ; divide the remainder by the product of the time and principal, and the quotient will be the ratio.
Ε Χ Α Μ Ρ At what rate per cent. will £ 543 amount to 4705 18s. in 5 years ?
From the amount=705,9
Take the pric.cipal=543
At what rate per cent. will £391 175. amount to £449 35. 13,74qr. in 3 years ?
Anf. 14. 3. At what rate per cent. will £413 125. 6d. amount to £ 546 35. 8d. in 4 years ?
CA SE 4.
The amount, principal and rate per sent. given, to find the
Rule.-Subtrret the principal from the amount ; di. vide the remainder by the product of the ratio and prin. cipal ; and the quotient will be the time.
E x A M P L £ s.
1. In what time will £ 543 amount to £705 18s. at £6 per cent. per annum ?
From the amount=705,9
Take the principal=543
In what time will £ 3000 amount to £ 3810 at 41 per cent. per annum ?
Anf. 6 years.
To find the Interest of any sum, at 6 per cent. per annum,
for any number of months. ROLE.-If the months be an even number, multiply the principal by half that number : And if the months be uneven, halve the even months, to which annex is; thus, the half of 19 is 9,5, and multiply the principal as hefore, cutting off two figures more at the right hand, than there are decimals in both factors, which reduce to farthings, each time cuttirg off as at first.
4. What is the interest of £ 345. 16s. 6d. for 9 years and 11 months, at 6 per cent. per annum?
Amount=2551 11 91 A Table of Decimal parts for every day in the twelft.);
part of a year, which consists of 365 days. days (dec. pts days dec. pts. days dec. pts. days dec. pts days dee. pos. ,033 7 ,23 | 13; 1427 119!,624 | 251,
,82 1 8,263 | 14 946 20,657 25, ,854 3,098
9,296 | 15 2493 211,69 27,887 4 ,131 10 ,328 | 16,526 | 22,723.
,92 51;164 11,361 17,558 231,756 2911953 18,591 | 241,788
30 986 · Nore. This table may also be used for the parts of a year, in compound intereft, after having worked for whole years. To find the Interest of any sum, either for Months, or
Months and Days, at 6 per cent. per annum. RULE.-Multiply the principal by the number of months (and parts, if any, answering to the given number of days in the table) and cut off one figure at the right hand of the product more than is required by the rule in decimals, and the product will be the intereit for
the given time in fhillings and decimal parts of a snilling
What is the interest of £250 10s. for 19 months and 7 days?
7515 5010 22545 2505
Anf. s. 481,7115
=£24 Is. 8 d.
dosler Method of calculating Interest for Monihs, at £6
per cerit. per annum. Rule.--If the principal consist of pounds only, cut off the unit figure, and, as it then stands, it will be the interest for one inonth in ihilings and decimal parts : If it couts of pounds, shillings, &c. reduce the shillings, &c. to decimals, which, with the unit figure of the pounds, will be decimal parts of a shilling.
SIMPLE INTEREST IN FEDERAL MONEY.
PROB. I. When the principal is given in lawful money, and the interest is required in federal money, at 6 per cent. per annum.
Rule.-Reduce the shillings, &c. to their equivalent decimal, by inspection, divide the whole by 5, and the quotient is the annual interest : Or, multiply the principal by 2, and the product (having the unit figure of the pounds cut off) will be the interest as before.
1. Required the annual interest of 5171. 35. 7.d. at 6 per cent. ?
35. =,15 5)517,181 Dols. c. m. lid. 30
103,436 = 103,43,6 Anfi: Excess of 12 =
Or, 517,181 ,181
Dols: c. m.
103,4362 = 103,43,67 2. Required the annual interest of 11. in dollars ?
20 cents, Ans:
PROB. 2. When the principal is given in lawful money, and the interest and amount are required in federal money, at 6 per cent.
Rule.Reduce the lawful money to federal, then divide the principal by 20, and that quotient by 5; add those quotients together, and they are the intereft ; or add thein to the principal, and their sum is the amount,