ITALIAN DIVISION. 5 5. Abbreviation in Division (the Italian method). A great saving of labour and time is effected by subtracting in all operations of Division as you proceed. This principle admits of very wide application and will be constantly used throughout this book. Its main applications are to Long Division (Simple and Compound), Division of Decimals, Greatest Common Measure, and Division-approximation. 1°. Long Division. Draw a line under the figures required for the first step in division. Multiply the divisor by the first figure of the quotient, subtracting as you proceed. Bring down the next figure and draw a line ast before. Repeat the same process of multiplication and immediate subtraction with the second figure of the quotient and so on. 2. Compound Division (Money, Weights, Measures). It is obvious that this principle may be applied and the above method used in all the actual dividing required in Compound Division of any sort. This method is plainly applicable to Decimals and should always be used. Example. 8765-432 ÷ 123.4. 1234 87654.32 | 71.03 1274 4032 330 The Decimalisation of Money, Weights, or Measures reduces Compound Division to Division of Decimals. 4°. Greatest Common Measure. An application of this method renders the finding of G.C.M. surprisingly brief. 6. The Decimalisation of Money. The conversion of s. d. f. into decimals of a £ often greatly simplifies many calculations-more especially it renders of much greater service the Methods of Immediate Subtraction and Approximation. In general it is sufficient to get any sum of money in decimals of a £ correct to 3 places, but it must be remembered that these places must be correct in the final answer. Hence it is often necessary to find the exact decimal of a £. The methods given here will enable the student after a little practice to decimalise at sight. 1°. To convert £. s. d. f. into £ and decimals of a £. (1) To three places. Multiply the shillings by 5. Put down the tens-figure of the product as 1st dec. place. Reduce d. f. to farthings, adding 1 if pence are 6d. or over. Add unit-figure of shillings-product to tens-figure of the farthings found and put down sum as 2nd dec. place. Put unit-figure of farthings as 3rd dec. place. (2) Completely. Obtain the first three places as in (1). To get the fourth Multiply 2nd by 4, carrying from the 3rd × 4. Put unit-figure of this result (mentally) in the 4th place to see if its multiplication by 4 will have any effect on the carrying from the 3rd × 4 to get the true 4th place. Put down the unit-figure (thus corrected or not) as 4th place. Repeat this process with the 3rd and 4th to get the 5th, and then with the 4th and 5th to get the 6th and so on. (Always carefully making the above correction when necessary.) Note 1. This correction can only occur when the last figure obtained (the figure on which the carrying depends) is 2 or 7. E.g. it can only occur in getting the 4th when the 3rd is 2 or 7, in getting the 6th when the 5th is 2 or 7. METHOD OF FIVE AND FOUR. 9 It does not always occur even then but it must be tried in these cases. If 2 or 7 does not occur at any stage this correction need not be considered. Note 2. This process brings 4999 ..... and therefore, practically, when 48 occurs or 49 after correction, change into 5 and end the decimal. Note 3. Observe-the 1st dec. place is left untouched. Note 4. If it is desirable to stop at any place and make allowance for the next it is easy to calculate it as above, and if it is found to be 5 or over add 1 to the place stopped at. Note 5. The operation of completing the Decimal given in (2) will be referred to as the method of Fours and the whole process of Decimalisation as the method of Five and Four. Note 6. The student will very quickly know when the repeating figure is reached—the forms which always occur are 416, 83, 916, or 5 (without recurrence). [Here 4x2=8 .. put (mentally) 0 in 5th place and see its effect on 2 x 4. This effect is of course nothing as 4x0=0.. no correction is needed.] 4×2=8+0=8=955208 and so on, the 3 obviously repeating. (0 carried from 4 × 0) |