FASTER SUBTRACTION.
Subtraction is often faster in two steps instead of one.
For example,
427 - 38 = (427 - 27) - (38 - 27) = 400 - 11 = 389.
A generic advice might be given as "First remove what's
easy, next whatever remains". Another example:
1049 - 187 = 1000 - (187 - 49) = 900 - 38 = 862.
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