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Midtiply 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.
s. d. qrs.
A note for 65 dollars, 31 cents, has been on interest 25 days; how much is the interest thereof in New-England currency? $ cts.
Ans. 65,31=6531 x 25=1,63275=1 7 2 REMARKS.--In the above, and likewise in the preceding practical Rules, (page 115) the interest is confined at 6
pei cent. which adınits of a variety of short methods of casting: and when the rate of interest is -7 per cent. as estaI:Vished in New York, &c. you may first cast the interest it
per cent. and add thereto one sixth of itself, and the sun ill be the interest at 7 per ct., which perhaps, many times
will be found more convenient than the general rule of cast ng interest.
Required the interest of 75l. for 5 months, at 7 per cent
7,5 for 1 month.
£. s. d.
Ans. £2 3 9 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.
1. What is the rebate of 50 dollars, for 6 months, ill 6 The interest of 50 dollars for 6 months, is
per cent. 3
1 51 And, the interest of 1 dol. 50 cts. for 6 months, is
Ans. Rebate, $1. 44 2. What is the rebate of 151. for 7 months, at 5 pes cent. ?
£. s. d. Interest of 1501. for 7 months, is
4 7 6 Interest of 41. 7s. 6d. for 7 months, is
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 in terest, 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 Federai Money. RULE. I.-Bring the given sum into a decimal oxpression by in. spection, (as in Problem I. page 80) then divido the whole by 3 in Now-England, and by ,4 in New-York currency, and the quotient will be dollars, cents, &c.
1. Reduce 541. 8s. 31d. New-England currency, to fos leral money.
,3)54,415 decimally expressed.
Ans. $181,38 cts. 2. Reduce 7s. 11 d. New-England currency, to federal noney. 7s. 11 d.=£0,399 then, ,3),399
Ans $1,33 3. Reduce 5131. 16s. 10d. New-York, &c. currency, to Federal money
4. Reduce 193. 5 d. New-York, &c. currency, to Fedemal Money
,40,974 decimal of 19s. 5 d.
$2,43, Ans. 5. Reduce 641. New-England currency, to Federal Money.
,3)64000 decimal expression.
$213,33 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.
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, anil the quotient will be cents.
1. Reduce 45s. 6d. New-England currency, to Federal Money.
6x8+2 = 50 to be annexed.
758 cents.=7,58 2. Reduce 21. 10s. 90. New-York, &c. currency, to l'ederal Money.
9x8+2=74 to be annexed. Then 8)5074
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 ciphers to the shillings; then divide as ber fore, &c.
33. Raduan 31. 55. New-England currency, to Federal Morey
31. Js --659. Then 6)6500
SOME USEFUL RULES,
FOR FINDING THE CONTENTS OF SUPERFICES AND SOLIUS.
SECTION 1.-OF SUPERFICES. The superfices or area of any plane surface, is compo sed or made
greater or less, according to the different measures by which the dimensions of the figure are taken or measured :—and because 12 inches ir length wake foot of long measure, therefore, 12 x 12=144 the square inches in a superficial foot, &c. Art. I. To find the area of a square having equal sides
RULE. Multiply the side of the square into itself and the prcduct will be the area, or content.
EXAMPLES 1. How many square feet of boards are contained in the floor of a room which is 20 feet
20 x 20=400 feet, the Answer. 2. Suppose a square lot of land measures 26 rods ca each side, how many acres doth it contain ?
NOTE.—160 square rods make an acre.
36 r. the Answer": Art. 2. To measure a parallelogram, or long square.
RULE. Multiply the length by the breadth, and the product will be the area, or superficial content.
EXAMPLES 1. A certain garden, in form of a long square, is 96 feet ong, and 54 wide; how many square feet of ground are contained in it? Ans. 96 X 5455184 square feet.
2. A lot of land, in form of a long square, is 120 rods in ength, and 60 rods wide ; how many acres are in it?
120 y. 60=7200 sq. rods, then 120=45 acres. Ans. 3. If a board or plank he 21 feet long, and 18 inches road ; how many square feet are contained in it?
18 inches=1,5 feet, then, 21 x1,5–31,5 Ans.
Or, in measuring boards, you may multiply the length in "eet by the breadth in inches, and divide by 12, the quoient will give the answer in square feet, &c.
Thus, in the foregoing example, 21 x 18:12=31,5 as pefore.
4. If a board be 8 inches wide, how much in length will make a square foot ? Rule.--Divide 144-by the breadth, thus, 8)144
13 in. 5. If a piece of land be 5 rods wide, how many rods in length will make an acre?
Rule.--Divide 160 by the breadth, and the quotient will be the length required, thus,
Ans. 32 rods in length.
EXAMPLES. 1. Required the area of a triangle whose base or longest side is 32 inches, and the perpendicular height 14 inches.
32x7=224 square inches the Answer. 2. There is a triavgular
or three cornered lot of land whose base or longest side is 51į rods; the perpendicular from the corner opposite the base measures 44 rods; how many acres doth it contain ?
51,5 x 22=1133 square rods,=7 acres, 13 rods.
* A Triangle may be either right angled or oblique; in either case the teacher can easily give the scholar a right idea of the base and perpendicu la, by marking it down on the slate, paper, &c.