To Subtract Any Number Consisting of Two Figures from 100.
Take the first figure from 9, and the second from 10. For example: in subtracting 73 from 100, or in taking 73 cents change out of a dollar, say 7 from 9 and 2, and 3 from 10 and 7, or 27 cents. Practice this rule. It is simple, and will be found particularly helpful in making change.