Find the three digit prime number.

Question

What is the largest three-digit prime each of whose digits is a prime? - I believe it is 773, but correct me if I'm wrong.

Answer 1

Well, it can't be $9xx$ because $9$ is not prime. Similarly, it can't be $8xx$. Thus you're left with $7xx$ or down.

$7$ is prime, and in reverse order, the first three primes of $7xx$ are $797, 787, 773$. The first two don't pass as they contain $8$ and $9$. Thus $773$ should be the largest such prime.