ADDITION AND SUBTRACTION. EXAMPLES. (3.) Add 5.634 21.321 .654 .012 5.364 32.985 (4.) (5.) COR. As the relation of the orders are the same, and the decimals rise in value in the same direction, whilst in name they take the opposite direction; hence, addition and subtraction of decimals are performed as in Integral Numbers. MULTIPLICATION. THEOREM. In the multiplication of decimals, the product will have as many places of decimals as both factors. to x t = Tho .1 x .1 = .01, and Ito x t = robo .01 x.1= .001. 1ST COL. 2D COL or, 1 x 1 = 1 and 1 x.1 = .1 .1 x 1 = .1 and .l' x1 = .01 .01 x 1 = .01 and .01 x .1 = .001 The first column of products is the same as the first column of multiplicands, as 1 is the multiplier. The multiplier in the second case is one-tenth, consequently the products of the second column must be one-tenth of the first. Therefore the product of two decimal factors will have as many decimal places as both factors. 1 x 1 1, units. 1 x 1 = 1, units. REM.—Observe the correspondence in name, when the contrary orders are multiplied. PROBLEMS. 2. Multiply .534 1. Multiply 3.156 .215 15780 3156 6312 .678540 3204 1602 534 .072624 REM.—Each product must have six decimals, hence in the second example a zero must be prefixed. DIVISION Corollaries to Theorem, Page 34. COR. 1.-As the product of the divisor and quotient is equal to the dividend, therefore the dividend has as many decimal figures as both divisor and quotient. COR. 2.-If the divisor has decimal figures and the dividend has none, or less than the divisor, as many must be added to the dividend as to make the number equal to that of the divisor, and then the quotient will be integral. If more decimals are added to the dividend, the quotient will contain as many. PROBLEMS. 1. Divide 21.4263 by 3.12. 3.12 ) 21.4263 ( 6.86+ As the divisor has two 18 72 places of decimals, the 2 706 quotient will be integral 2 496 for two places of decimals 2103 in the dividend ; after that 1872 the quotient will be deci231, remainder. mal. 2. Reduce the fraction ; to a decimal. 4 ) 1.00 3 5) .6 COR.-Any common fraction may be reduced to a decimal by performing the division indicated by the terms. EXAMPLES. 1. Multiply 1 by .1; by .01; by .001; by .0001. 2. Multiply .1 by .1; by .01; by .001; by .0001. 3. Multiply .2 by 2; .03 by.4; .05 x .04; .06 x .003; and .003 x .004. 4. Multiply 4.732 by .345. 5. Multiply 2.074 by .021. 6. Multiply 3.541 by .002. 7. Multiply .002 by .3754. 8. Multiply 721.56 by 21.42. 9. Multiply 642.54 by 2162. 10. Multiply 756.48. by 4635. REM.—Prove the last seven examples by division. PRACTICAL EXAMPLES. 1. A merchant sold 205 yards cotton cloth at $.125 per yard, 75 yards gray flannel at $.625 per yard, 12 pairs hose at $.375 per pair, 54 yards linen at $.555 per yard. What was the amount of the bill ? Ans. $106.97. 2. Bought five tracts of land ; viz., 237 acres at $57.43 per acre, 326 acres at $49.02 per acre, 431 acres at $31.21 per acre, 1274 acres at $12.48 per acre, and 21346 acres at $2.045 per acre. The whole is to be paid in three equal instalments ; how much is each payment? Ans. $34198.344. This table of aliquot parts enables us to shorten the operations of multiplication and division. 10 cts. = $1. 175 cts. = 66 cts. = $$ 20 cts. = $1. 121 cts. = $1. 374 cts. = $3. 25 cts. = $1 16 cts. = $7. 621 cts. = 50 cts. 334 cts. = 874 cts. = $5. EXAMPLES. 1. Multiply 576 by 100. Ans. 57600. 2. Multiply 576 by 25. 576 x 100 = 14400. 3. Multiply 576 by 50. 576 x 100 = 28800. 4. Divide 576 by 100. Ans. 5.76. 5. Divide 576 by 50. 576 ; 190 = 576 x 2 = 100 = 11.52. 6. Divide 576 by 25. 576 ; 100 = 576 x 4 = 100 = 23.04. 7. Divide 67453.2645 by 47.215. SOLUTION. 47215 202182 133226 387964 102445 8015 There must be one decimal in the quotient; for 3 in divisor + 1 in quotient = 4 in dividend. |