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UKMT Junior Mathematical Challenge, 2019

Number theory Difficulty 1.0 Junior Find the answer United Kingdom

Emily writes down the largest two-digit prime such that each of its digits is prime. Krish writes down the smallest two-digit prime such that each of its digits is prime. Kirsten subtracts Krish's number from Emily's number. What answer does Kirsten obtain?

(A) $14$ (B) $20$ (C) $36$ (D) $45$ (E) $50$

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