Remembrance of subtraction of a single digit from a single digit or from the numbers such as 10, 11, 12, ----17, 18 is necessary beside the single digit additions.
0 - 0 = 0
1 - 0 = 1
1 - 1 = 0
2 - 0 = 2
2 - 1 = 1
2 - 2 = 0
3 - 0 = 3
3 - 1 = 2
3 - 2 = 1
3 - 3 = 0
4 - 0 = 4
4 - 1 = 3
4 - 2 = 2
4 - 3 = 1
4 - 4 = 0
5 - 0 = 5
5 - 1 = 4
5 - 2 = 3
5 - 3 = 2
5 - 4 = 1
5 - 5 = 0
6 - 0 = 6
6 - 1 = 5
6 - 2 = 4
6 - 3 = 3
6 - 4 = 2
6 - 5 = 1
6 - 6 = 0
7 - 0 = 7
7 - 1 = 6
7 - 2 = 5
7 - 3 = 4
7 - 4 = 3
7 - 5 = 2
7 - 6 = 1
7 - 7 = 0
8 - 0 = 8
8 - 1 = 7
8 - 2 = 6
8 - 3 = 5
8 - 4 = 4
8 - 5 = 3
8 - 6 = 2
8 - 7 = 1
8 - 8 = 0
9 - 0 = 9
9 - 1 = 8
9 - 2 = 7
9 - 3 = 6
9 - 4 = 5
9 - 5 = 4
9 - 6 = 3
9 - 7 = 2
9 - 8 = 1
9 - 9 = 0
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Due to the necessity of borrowing 1 from the previous place, which is ten times of the respective current place, situations such as subtraction of 18 - d, 17 - d, ---, 11 - d and 10 - d arise.
When at the place in the upper number is 8 and below that is 9 to be subtracted, then we have to borrow 1 making it 18, and the subtraction becomes as 18 - 9, naturally we need not think much, we must recollect 18 - 9 = 9.
Similarly, when at the place in the upper number is 7 and below that is either 9 or 8 to be subtracted, then we have to borrow 1, making the subtraction as 17 - 9 or 17 - 8, we must be able to get instantly: 17 - 9 = 8 or 17 - 8 = 9; and so on.
When at the place in the upper number is 8 and below that is 9 to be subtracted, then we have to borrow 1 making it 18, and the subtraction becomes as 18 - 9, naturally we need not think much, we must recollect 18 - 9 = 9.
Similarly, when at the place in the upper number is 7 and below that is either 9 or 8 to be subtracted, then we have to borrow 1, making the subtraction as 17 - 9 or 17 - 8, we must be able to get instantly: 17 - 9 = 8 or 17 - 8 = 9; and so on.
18 - 9 = 9
17 - 9 = 8
17 - 8 = 9
16 - 9 = 7
16 - 8 = 8
16 - 7 = 9
15 - 9 = 6
15 - 8 = 7
15 - 7 = 8
15 - 6 = 9
14 - 9 = 5
14 - 8 = 6
14 - 7 = 7
14 - 6 = 8
14 - 5 = 9
13 - 9 = 4
13 - 8 = 5
13 - 7 = 6
13 - 6 = 7
13 - 5 = 8
13 - 4 = 9
12 - 9 = 3
12 - 8 = 4
12 - 7 = 5
12 - 6 = 6
12 - 5 = 7
12 - 4 = 8
12 - 3 = 9
11 - 9 = 2
11 - 8 = 3
11 - 7 = 4
11 - 6 = 5
11 - 5 = 6
11 - 4 = 7
11 - 3 = 8
11 - 2 = 9
10 - 9 = 1
10 - 8 = 2
10 - 7 = 3
10 - 6 = 4
10 - 5 = 5
10 - 4 = 6
10 - 3 = 7
10 - 2 = 8
10 - 1 = 9
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These subtractions are easy. However, one must read repeatedly, try to recollect and use in solving exercises involving these subtractions; without the use of any electronic device, and have practice to attain the best speed.
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