The rule of PRACTICE is so called from the great facility it affords in calculation, and from its general use among merchants and tradesmen. It is a short and concise method of computing the value of commodities by taking aliquot parts. An aliquot part of a number is such a part as, being taken a certain number of times, will produce the number exactly; thus 6s. 8d. is the third, or aliquot part of a pound; 3d. is the fourth, or aliquot part of a shilling, and so on, as demonstrated in the foregoing Tables. cent. annum is at the rate of 1d. 2 per cent. per annum is at the rate of find the interest or discount at 5 month for £1, d. ditto; hence to For Hundred-weights and Tons. cent. is very easy. 10 11 5 2 8 102 13 4 5 12 0 112 0 0 The sum total of 100,000 farthings, in money of account, is ascertained by dividing by 4, 12, and 20: thus 4)100,000 farthings. 12)25,000 pence. 20) 2,083 shillings. £104 3s. 4d. The Root of any power is such a number as, being multiplied into itself a certain number of times, will produce that power. Roots... 1 2 3 4 5」 6」 7」「 8」「9 「10 | 11 | 12 Squares 14 9 16 25 36 49 64 81 100 121 144 Cubes... 1 8 27 64 125 216 343 512 729 1000 1331 1728| RULES FOR MENTAL CALCULATION. MULTIPLICATION. (1) To Multiply by 10. Add a nought. 6 x 10 = 60. (2) To Multiply by any number of tens-20, 30, etc. Add a nought, and multiply by the number of tens. (4) To Multiply by any number of hundreds-200, 300, etc. Add two noughts, and multiply by the number of hundreds. 600 × 2 =3 1200. 6 x 200 = (5) To Multiply by any number of tens, hundreds, or thousands. Add the nought or noughts, and multiply by the number of tens, hundreds, or thousands. (6) To Multiply by 5. Multiply by 10, and divide by 2. 6 x 5 = 60 ÷ 2 = 30. (7) To Multiply by 15, 35, 45, or 55. Multiply by twice the multiplier, and divide by 2. 6 X 702 6 x 15 6 x 35 6 × 45 = 6 X 55 = = 6 X 90 ÷ 2 = 5402270. (8) To Multiply by 75 (75 300 ÷ 4). Add 2 noughts, multiply by 3, and divide by 4. 1800 ÷ 4 = (9) To Multiply by 125 (125 = 1000 ÷ 8). Add 3 noughts, and divide by 8. = 450. = 1000 ÷ 4). (10) To Multiply by 250 (250 6 X 250 6000 ÷ 4 = 1500. (11) To Square a number (to multiply it by itself). Add the number to its unit figure, multiply by the tens, and add the square of the unit figure. Cut off the end figure, which will be the remainder. Cut off the two end figures, which will be the remainder. 627 100 6, 27 = 6.2. (3) To Divide by 1000. Cut off the three end figures, which will be the remainder. 6127 1000 = (4) To Divide by 25. 6, 1276127. Multiply by 4, and divide by 100. Divide the remainder by 4. (6) To Divide by any number of tens, hundreds, or thousands. Cut off as many end figures as there are noughts, and divide by the number of tens, hundreds, or thousands. CALCULATION OF PRICES. (1) To find the price of a dozen articles. Call the pence shillings, and every farthing 3d. 31d. = 38. = 3s. 3d. 31d. = 38. 6d. 3 d. 38. 9d. When the price exceeds a shilling, reduce shillings to pence. 1 doz. articles at 1s. 6d. = 1 doz. at 181d. (2) To find the price of any number of dozens. = 188. 3d. Find the price of one dozen, and multiply by the number of dozens. 5 dozen articles at 2s. 1d. =25s. 6d. × 5 = £6 7s. 6d. A gross is 144 or 12 dozen. (3) To find the price of one article, the price of a dozen being given. Call the shillings pence, and every threepence a farthing. The price of one article at 10s. 3d. per dozen = 101d. (4) To find the price of 20 articles. Call the shillings pounds, and every threepence five shillings. 20 articles at 2s. 3d. = £2 5s. (5) To find the price of 240 articles. Call the pence pounds, and every farthing five shillings. (6) To find the price of 480 articles. Call the pence pounds, and multiply by 2. 480 articles at 5d. = £5 10s. × 2 = £11. (7)_ To find the price of 960 articles. Reduce the price of one to farthings, and call farthings pounds. 960 articles at 24d. = 10 farthings = £10. |