Subtracting from 1,000
To subtract a large number from 1,000 you can use this basic rule: subtract all number from 10, then subtract 1 from each number except the last number:
1000
-378
step1: 10 - 3 = 7 (- 1) = 6
step2: 10 - 7 = 3 (- 1) = 2
step3: 10 - 8 = 2
answer: 622
Two digits subtraction
To subtract a single digit number from a double digits number: you can subtract 10 from the double digit number first, then add the number pairs with the single digit number that added to 10:
35
-8
step1: 35 - 10 = 25
step2: 10 - 8 = 2
step3: 25 + 2 = 27
answer: 27