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Today Puzzle #675

Puzzle No. 675– Thursday 13 February 2020

To celebrate his birthday, Bobby is asking you to work out his current favourite number. Like Johnny Ball's 1970s TV show, Bobby is thinking of a number. His two-digit number is a prime number. When the digits are reversed, it is still a two-digit prime number. The sum of both two-digit numbers adds up to the number of modern constellations in the sky. Assuming he picks the smaller of the two possible two-digit numbers, what is Bobby's current favourite number?

Today’s #PuzzleForToday has been set by Bobby Seagull, school maths teacher, author and Cambridge University Doctorate student.

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17.

17 and 71 are the two prime numbers. Added together, they make 88 which is the number of constellations in the sky.

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