TAE RATE PER CENT., INTEREST, AND PRINCIPAL BEING GIVEN, TO FIND THE TIME. Rule.- Place the interest of the given principal for one year opposite 12: then opposite the given interest will be the answer in months and decimals of a month. Or, place the interest of the given principal for one year opposite 365: then opposite the given interest will be the time in days. Example.—Gave 87,5 cents at 7 per cent. for $50.00 : how long did I have it? The interest of $50.00 for one year, is $3.50. Place 3.50 opposite 12: then opposite •875 is the answer, 3 months. Gave 24 cents at 7 per cent. for the use of $50 : how long did I have it? Place $3.50 opposite 365: then opposite 24 is the answer, 25 days. COMPOUND INTEREST. RULE.—Place the principal opposite fig. 1: then opposite the rate per cent. added to 100, on the fixed part, is the amount for one year. Place this amount opposite fig. 1: then opposite the same point is the amount for two years. Place this last amount oppoșite 1: then opposite the same point is the amount for 3 years, &c. years at 6 Example.- What is the compound interest on $5.00 for 5 per cent? Place 5 opposite 1: then opposite 106, (the por cent. added to 100,) is $5.30, the amount for 1 year. Now place $5.30 opposite 1: then opposite 106 is $5.62, the amount for 2 years. Now place $5.62 opposite fig. 1: then opposite 106 is $5.95, the amount for 3 years. Now place $5.95 opposite fig. 1: then opposite 106 is $6.31, the amount for 4 years. Now place $6.31 opposite fig. 1: then opposite 106 is $6.69, the amount for 5 years. LOSS AND GAIN. Bought a hogshead of molasses for $60: for how much must I sell it to gain 20 per cent. ? RULE.—Place 20 opposite 1: then opposite 60 is what must be added to the original cost to gain said per cent., viz... 12: which added to 60=72. Bought cloth at $2.50 per yard; but, being damaged, I am willing to sell it so as to lose 12 per cent. How must I sell it per yard ? Place 12 opposite 1: then opposite $2.50 is 30, the amount to be deducted from $2.50, which will leave 2:20, the answer. Bought cloth at 50 cents per yard : sold it for 10 cents advance from cost. What per cent. did I make ? Place 10 opposite 50 : then opposite 1 is 20 per cent., the answer. ANOTHER METHOD.--Place the original cost oppo. site 1: then opposite the rate per cent. added to 100, is the answer. Example.—Bought corn at 50 cents per bushel: at how much must I sell it to gain 20 per cent. ? Place 50 opposite 1: then opposite 120, is 60 cents, the answer. Bought cloth at $2 per yard, and sold it at $3 per yard: what per cent. did I make ? Place 2 opposite 1: then opposite 3 is 150, 50 per cent., answer. RULE OF THREE, OR PROPORTION. Rule.—Place the second term opposite the first : then opposite the third term, is the answer. Example.-If 2 yards of cloth cost $4.00, what cost 8 yards ? Place 4 opposite 2: then opposite 8 is 16. Note.-All numbers of yards at that rate, are now on the scale, and may be determined without moving the circular. At f of a dollar per yard, what cost 4 yards ? Place 7 opposite 8: then opposite the given num. ber of yards, is the answer. If 1 ton of hay cost $3.00, what cost 900 pounds ? Place 8 opposite 2000, (the number of lbs. in a ton:) then opposite 900 is the answer; and so of any other number of pounds. FELLOWSHIP. RULE. ---Place the whole gain or loss opposite the whole stock: then opposite each man's share of the stock is his share of the gain or loss. Example.--A invested $30, B invested $20, and they gained in trade $12: what is each one's share of the gain? Place 12 (the whole gain) opposite 50 (the whole stock): then opposite 20 (A's stock) is $4.80; and opposite 30 (B's stock) is $7.20. EVOLUTION. TO EXTRACT THE SQUARE Root. RULE.-Move the given number around until it is opposite the same number which is opposite 1; and that number is the answer sought. Example.- What is the square root of 42 ? Move 42 on the circular around until it comes opposite 6:48. Now 6.48 is opposite 1: hence that is the square root of 42. TO EXTRACT THE CUBE Root. RULE.—Move the given number around until it comes opposite a number, the square of which at the same time is opposite 1; and that number is the root sought. Example.—What is the cube root of 27 ? Move 27 around until it comes opposite 3: at that time 9 is opposite 1: hence 3 is the answer. TO APPORTION TAXES. RULE. Place the whole tax to be raised, found on the circular, opposite the whole valuation : then oppo. site each man's valuation, is his tax. Example.-A tax of $1.500.00 is levied on a val. uation of $200.000.00: what is a man's tax whose valuation is $700.00 ? Place 1500 opposite 200.000 : then opposite 700 is $5.25, the answer. SCHOOL Tax. 1550 days have been sent, and $33.20 tax is to be raised: how much is each man's tax ? Place 33.20 opposite 1550 : then opposite the days each man has sent is his tax. A has sent 28 days: his tax is 60 cents. Opposite 70, the number of days B has sent, is his tax, $1.50; and so of every other man's tax, without moving the scale. |