All from 9 and the last from 10

The formula ALL FROM 9 AND THE LAST FROM 10 is used to perform instant subtractions.

For example 1000 - 357 =?

We simply take each figure in 357 from 9 and the last figure from 10.

So the answer is 1000 - 357 = 643

This always works for subtractions from numbers consisting of a 1 followed by naught: 100; 1000; 10,000 etc.

Similarly, 10,000 - 1049 = 8951

 

For 1000 - 83, in which we have more zeros than figures in the numbers being subtracted, we simply suppose 83 is 083.

So, 1000 - 83 becomes 1000 - 083 = 917.