THE 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 opposite 1 then opposite the same point is the amount for 3 years, &c. Example. What is the compound interest on $5.00 for 5 years at 6 per cent ? Place 5 opposite 1: then opposite 106, (the per 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 ycars. 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 opposite 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 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 $8.00, 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 valuation 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. |