# Hard Dice Probability Question

Alexi rolled four standard dice and lined them up to create a 4-digit number. He removed two dice from the line and rolled them again. Alexi then returned each re-rolled die to its original position in the line, thereby creating a new 4-digit number. The probability that the new 4-digit number is greater than the original 4-digit number can be expressed as a fraction $$\dfrac{a}{b}$$, where $$a$$ and $$b$$ are relatively prime integers. What is $$a$$ + $$b$$?

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