Khan/khan-exercises — pull request #5456 by elizabethslavitt (2011-11-03 00:24:07+00:00)
Title: Subtraction changes

Updated subtraction 2-4:
Sub 2: Changed to 2-3 digit # minus 2-3 digit number, no borrowing (was 2 digit minus 2 digit with some borrowing)
Sub 3: Changed to 2-4 digit number minus 2-4 digit number, with borrowing 1x per problem. No subtraction from zero (was 3-digit minus 3-digit with some borrowing)
Sub 4: Changed to 2-4 digit number minus 2-4 digit number, with borrowing 2x per problem and subtraction from 0 (was 4-digit minus 4-digit with some borrowing)