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UKMT Senior Mathematical Challenge, 2015

Number theory Difficulty 2.0 Junior Find the answer United Kingdom

The numbers 5, 6, 7, 8, 9, 10 are to be placed, one in each of the circles in the diagram, so that the sum of the numbers in each pair of touching circles is a prime number. The number 5 is placed in the top circle. Which number is placed in the shaded circle?

(A) $6$ (B) $7$ (C) $8$ (D) $9$ (E) $10$

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