Question

Which one of the 4 red digits will make all 3 #’s prime

Answer 1

1

Explanation:

9 can't be the answer because 39 is not a prime number

3 can't be the answer because 33 is not a prime number

5 can't be the answer because 75, 35 and 15 are not prime numbers

1 is the answer because 71, 31 and 11 are all prime numbers

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