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UKMT Junior Mathematical Challenge, 2019

Number theory Difficulty 2.0 Junior Find the answer United Kingdom

Tamsin writes down three two-digit integers. One is square, one is prime and one is triangular. She uses the digits $3, 4, 5, 6, 7$ and $8$ exactly once each. Which prime does she write?

(A) $37$ (B) $43$ (C) $53$ (D) $73$ (E) $83$

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