Subtracting Techniques

Here’s a basic rule to subtract a large number from 1,000: 

1.) First, subtract every digit [except the last] from 9 

2.) And then, subtract the last digit from 10 

For example: 1,000 – 556 

Step 1: 9 - 5 = 4 

Step 2: 9 - 5 = 4 

Step 3: 10 - 6 = 4 

The answer is: 1,000 - 556 = 444.