Vedic maths - subtraction by compliment
step 1 - all from nine
step 2 - last from 10
example 1 - 100 - 23 = 77
9-2=7
10-3=7
So the final answer will be 77
example 2 - 1000 - 284 = 716
9-8=1
10-4=6
So the final answer will be 716
example 3 - 10000 - 3904 = 6096
9-3=6
9-9=0
9-0=9
So the final answer will be 6096