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The reason the answer is always 1089 is because the tens numbers (of the subtraction) are always the same and the top number in the ones column (of the subtraction) will always be smaller so you have to borrow from the tens column making the top tens number one less. Then you have to borrow from the hundreds column making it nine more than the bottom tens number so when you take the bottom tens number (of the subtraction)off of the top tens number (of the subtraction) you will get nine. When you swap them around to add the answer together the hundreds and ones will always be number bonds to nine and when you add nine and nine it equals eighteen so you carry the one and when you add nine and one it equals ten which is why the answer is 1089