CHAPTER II SUBTRACTION 10. Drill Tables. Daily practice on the following subtraction combinations will increase your speed and accuracy. Drill on these combinations until you can state all of the results in any order in less than thirty seconds. Drill on the following until you can state all of the results in any order in less than thirty seconds. 8 01 201 8 9 4 16 14 15 18 13 17 12 11 16 11 12 6 9 15 16 6 11 9 3 37 24 13 14 14 17 11 14 15 14 12 11 11 9 2 8 7 In subtraction "borrowing" is frequently necessary. Perform the subtractions indicated; check the first five by method (a), and the last five by method (b), Always check results in substraction. 11. The following data show the sales in the various departments of a large store for the month of August, 1921, and the month of August, 1922. Enter the sales in the proper column of the blank. Find the increase or decrease in the amount of the sales in each department for August, 1922, over the sales in the same department for August, 1921. Enter increases in black ink; decreases in red ink. Find the net increase for the entire store. Do the results check? 12. The following shows the total population of the United States for the years indicated. Rule a blank form to show the year the census was taken, the population each census year, and the increase in population for each interval of 10 years. See how simple you can make this blank. Check the results. 13. Rule a form, enter the following statistics, find the gross profit of each department, and the gross profit of the entire store. 14. Rule a suitable form, enter the following statistics, and find: a. The gross profit by departments. b. The gross profit of the entire store (two ways). c. The net profit or net loss by departments; enter net profit in black, net loss in red. d. Net profit or net loss of the entire store (two ways). 12. Subtracting by Adding Complements. A series of additions and subtractions may be performed by the method of adding complements. The complement of a number is the number which must be added to get the next higher power of ten. Thus, the complement of 6 is 4; the complement of 83 is 17. If, instead of subtracting a number less than ten from a given number, its complement be added, the result will be 10 too large. Thus, 136 7 or 13 + 4 = 17 (a result 10 too large). = If, instead of subtracting two numbers less than ten from a given number, their complements are added, the result will be 20 too large; if the complements of three such numbers are added, the result will be 30 too large, etc. SOLUTION. 38 +6 + 3 + 2 = 49 Since three complements were added, subtract 30, leaving 19. 3. 4684-7 = ? SOLUTION. 46 +2 + 4 +3 be subtracted, leaving 35. = 55. Since two complements were added, 20 must The practical value of this method will be shown by the following examples. 1. 36 – 24+ 19 − 12 + 21 – 13 – 6 36 - 24 19 - 12 21 13 6 21 SOLUTION. By combining as indicated in the units' column, beginning at the top (complements are marked with an *) we have Since four complements were added, the result is 40 too large. Therefore write 1 and drop the 4. By combining as indicated in the tens' column we have 3+8* + 1 + 9* + 2 + 9* = 32 Since three complements were added, the result is 30 too large. Write 2 and drop the 3. Result, 21. |