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Copy the numbers in lines 25 to 35 inclusive, and add; then add the columns numbered 36 to 43 inclusive:

36. 37. 38.

25.

2

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26. 1

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3

28.

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29.

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58. 59. 60. 61. 62. 63.

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Proceed in the same way for lines numbered 44 to 57 inclusive, and for columns numbered 58 to 65 inclusive:

4880

41.

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8

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546 31

23. Addition of Digits. You have already learned how to add digits, but the following directions will help you:

(1) First add from the bottom upwards and write the sum. (2) Then add from the top downwards, to see that you have made no mistake.

This is called checking the result, and is very important in all calculations.

(3) Try to group digits in adding, thus allowing you to work more rapidly.

For example, in this case we may begin with 6 and add each digit in order, thinking thus: "6, 15, 18, 25, 29." It is better, however, to look at the 6 and 9 and think "15"; then look at the 7 and 3 and think of 10 as added to the 15, saying to ourselves "25"; then to look at 4 and think " 29.”

EXERCISE 5

Add the following, checking your work and timing yourself:

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24.

Copy the numbers in lines 25 to 35 inclusive, and add; then add the columns numbered 36 to 43 inclusive:

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44. 1

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49. 1

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58. 59. 60. 61. 62. 63. 64.

6

3

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5

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6

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2

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3 21

40.

3

8

4

4

1

9

23

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1

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Proceed in the same way for lines numbered 44 to 57 inclusive, and for columns numbered 58 to 65 inclusive:

3

8

8

4

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354

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24. Addition of Two-Figure Numbers. You have also learned how to add two-figure numbers, but the following directions may help you to understand the work:

(1) Write the addends so that units of the same order are in the same column.

(2) Add each column by itself, beginning at the right, and write the sum, if it is less than 10, under the column added.

(3) If the sum of any column is 10 or more, write the unit figure under the column added, and add the tens with the next column.

1.

21

32

46

7.

34

62

81

92

This is done in full in the example shown above. In practice, however, we do not write the sum of each column by itself, but proceed as here shown. We think of the work as follows: "4, 10, $67 17," writing the 7 and adding the 1 to the tens' column; 86 then think: "1, 4, 12, 18," and write the 8 under the tens' column and the 1 in the hundreds' place.

34

$187

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The dollar sign before the top number in a column indicates that all the numbers in the column represent dollars.

EXERCISE 6

Add the following and check your work:

3.

4.

6

34

57

9

61

68

8.

62

48

31

43

67

86

34

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17 sum of units 17 sum of tens 187 sum

10.

62

48

8

75

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