Question

The integer 113 is a prime, and its reverse 311 is also a prime. How many twodigit
primes are there between 10 and 99 which have the same property?

Answer 1

since primes must end in 1,3,7,9 there are only a few decades to check.

Answer 2

13 and 31 , 17 and 71 , 19 and 91 , 37 and 73 , 79 and 97 .