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Number theory Difficulty 3.0 AMC 10/12 Find the answer United Kingdom

In the four-digit number ' $PQRS$ ', the digits $P$ , $Q$ , $R$ and $S$ are all non-zero and are in increasing order from left to right. What is the largest possible difference ' $QS$ ' $-$ ' $PR$ ' between the two two-digit numbers ' $QS$ ' and ' $PR$ '?

(A) $86$ (B) $61$ (C) $56$ (D) $50$ (E) $16$

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