Question

Let ab, a ≠ b, is a 2-digit prime number such that ba is also a prime

number. The sum of all such numbers is:

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Answer 1

The number A-B and A+B both are either even or odd.However they are also both prime.

So they must be odd.Therefore one of A & B is odd and the other is even.

Because A is Prime between A & B .A must be odd prime .Therefore B = 2, the

only even prime . so A-2, A and A+2 are consecutive odd prime and thus must be

3,5 , 7 .

The sum of four prime = 2+3+5+7 = 17 is the prime number