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This problem trains for: SAT-I, AMC-8, GMAT.

Find the negative difference of two numbers a and b, knowing that their sum is 7007 and one of them can be found by adding three zeroes at the end of the other one.

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Given some numbers, we can always order them. We may assume a is larger than b without loss of generality. Then,

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Then:

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The negative difference is -6993.