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RULE. As the months, weeks, or days in a year, Are to the interest of the given sum for one year; So are the months, weeks, or days in the given time, To the interest required.

Or, take parts of the yearly interest for the aliquot parts of a year that are in the given time, and add the interest for the odd days (if any) found by the Rule of Three.

EXAMPLES. 1. What is the interest of 350L. for 3 years and 10 months, at 6L. per cent. per annum? Ans. 80L. 10s L.

M. L.

Y. M. 350

12: 21 3 10 6

46 12

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80L, 10s. 2. What is the interest of 150L. 19s. for 3 years and 4 months, at 6L. per cent. per annum? Ans. 30L. 3s. 9d.

3. What is the interest of 57L. 17s. 8d. for 3 months, at 6L. per cent. per annum?

Ans. 175. 4d. 4. What is the interest of 7500 dollars for 4 months, at 7 dollars per cent, per annum?

Ans. $175.00. 5. What is the interest of 400 L. for 1 week, at 5L. per .cent. per annum ?

Ans. 7s. 8 d.t 6. What is the interest of 126L. 125. for 16 weeks, at 4 L. per cent. per annum?

Ans. IL. 155. 0. dot.

7. What is the interest of 250L. for 73 days, at 7L. per cent. per annum?

Ans. 3L. 10s. 8. What is the interest of 500L. for 146 days, at 6L. per cent. per annum?

Ans. 12L. 9. What is the interest of 71L. 3s. 11 d. for 1 year, 5 months, and 25 days, at 6L. per cent. per annum?

Ans. 6L. 6s. 10d. 10. What is the amount of a bond for 967 dollars for 2 years and 4 months, at 6 dollars per cent. per annum

?

Ans. $1102.38. Note 1.-The interest of any sum for any number of months, may be concisely found by the following

RULE,

Multiply the principal by half the number of months, and divide the product by 100; or, multiply the principal by the whole number of months, divide the product by 2, and divide the quotient by 100; the result by either operation, will be the interest at 6 per cent. per annum.

For the interest at any other rate per cent. take aliquot parts of the interest at 6 per cent. and add, or subtract, as the case requires.

EXAMPLES.

1. What is the interest of 450L. for 8 months, at 6L. per cent. per annum; and also at 7L. per cent. per annum? L. · Or thus:

L.
450
450

18 interest at 6
3 interest at 1 per cent.

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per cent,

L. 18100

2)3600

L.21 interest at 7 per cent.

L. 1800 2. What is the interest of 900L, for 8 months at 6L. per cent. per annum?

Ans. 36L. 3. What is the interest of 450L, for 4 months, at 7L. per cent. per annum? ·

Ans. TOL. 10s. 4. What is the interest of 148L. 12s. 6 d. for 11 months, at 6 per cent. per annum ?

Ans. 8L 35. 5 d. 5. What is the interest of 1260 dollars for 4 months, at 6 dollars per cent. per annum; and also at 7 per cent. per annum?

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$ 25.20 6. What is the interest of 630 dollars for 8 months, at 6 dollars per cent. per annum?

Ans. S 25.20. 7. What is the interest of 7342 dollars for 16 months, at 6 dollars per cent. per annum?

Ans. 5587.36. 8. What is the interest of 750 dollars for 9 months, at 7 dollars per cent. per annum?

Ans. $ 39,371 9. What is the interest of 375 dollars for 5 months, at 6 dollars per cent. per annum?

Ans. $ 10.311 Note 2.-When the principal is dollars and cents, multiply by the whole number of months, divide the product by 2, and separate one figure from the right of the quotient, as a remainder or fraction; the figures on the left of this will be the interest in mills.

10. What is the interest of $425.98 for 3 months, at 6 dollars per cent. per annum; and also at 7 dollars per cent. per annum?

Dols.
425.98
| 6.38.9

int. at 6 per cent.
3

1

D.c.m.

2127794

$ 7.45.3 + int. at 7 per cent.

Interest in mills 638917

11. What is the interest of $ 460.50 for 4 months, at 6 dollars per cent. per annum?

Ans. $9.21. 12. What is the interest of $ 230,25 for 8 months, at 7 dollars per cent. per annum?

Ans. 810.745 13. What is the interest of $764.50 for 3 years and 10 months, at 6 dollars per cent. per annum? Ans. $175.83).

To find the interest of any given sum as computed at the banks, at 6 per cent.

RULE.

1. Multiply the dollars by the number of days, and di.

vide the product by 6; the quotient will be the interest in mills. Or,

2. If the principal be any number of dollars, the interest for 60 days, at 6 per cent. will be exactly that number of cents : and for the time more or less than 60 take aliquot parts.*

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1. What is the interest of 1542 dollars for 90 days, at 6 per cent. per annum? also, for 60,7 for 30, and for 20 days, at the same rate ? Dols.

30 | 1 | 1542 int.for 60 days in cts: 1542 90

20 771 int. for 30 days in cts..

6138780

514 int.for 20 days in cts.

D. cts. 23130 mills.

Or, int. for 60 days 15. 42. for 30

7.71. Or, $23.13 int. for 90 d.

for 20

5. 14. 2. What is the interest of 771 dollars for 90 days, at 6 per cent. per annum?

Ans. 8.11.5623. What is the interest of 3084 dollars for 30 days, at 6 per cent. per annum ?

Ans. $ 15.42. 4. What is the interest of 2324 dollars for 54 days, at 6 per cent. per annum?

Ans. 8 20.913+ 5. What is the interest of 3942 dollars for 50 days, at 6 per cent. per annum ?

Ans. $ 32.85.

CASE 5. To find the principal, when the amount, time, and rate per cent. are given.

* This is calculating after the rate of 360 instead of 365 days to the year, which will always make the interest rather too much.

If the interest found by this rule be divided by 73, the quotient will show by how much it exceeds the true interest.

+ When a note is drawn for 60 days, the interest is mostly calculated for 63, on account of three days, called days of grace, which are commonly allowed the payer, on all notes, after the

time expires for which they were drawn. The interest is here only computed for the given time.

K 2

RULE. As the amount of 100 pounds, or dollars, at the rate and time given,

Is to 190 pounds, or dollars ;
So is the amount given,
To the principal required.

EXAMPLES. 1. What principal at interest for five years, at 6 per cent. per annum, will amount to 650 L.? Ans. 500L. L.

L. L. L. 6

130 : 100 :: 650 5 years

100

L. 30 int, of 1001.. for 5 years.

130)65000(500 100

650

130 amt. of 100L. for 5 years.

00 2. What principal at interest for 10 years, at 6 per cent. per annum, will amount to 13001.. ? Ans. 812L. 10s,

3. What principal at interest for 4 years, at 5 per cent. per annum, will amount to $ 571 20 ? Ans. 476 dols.

CASE 6. To find the rate per cent. when the amount, time and principal are given.

RULE.
As the product of the time and principal,
Is to the interest for the whole time;
So is 100 pounds, or dollars,
To the rate per cent.

EXAMPLES 1. At what rate per cent. per annum, will 500L. amount to 650L. in 5 years ?

Ans. 6L. per cent. L.

L. L. L. 500 principal 650 amt.

2500 : 150 :: 100 5 years

ICO 2500 product. 150 int.

2500) 15000(6L.

15000

500 p

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