Skip to main content
OlympiadHQ

Browse · MATH

Print

jmc

number theory intermediate

Problem

How many prime numbers between 30 and 65 have a prime remainder when divided by 10?
Solution
If a prime number between 30 and 65 has a prime remainder when divided by 10, it must end in 3 or 7, since any number greater than 10 ending in 2 or 5 is composite. Systemically checking all possibilities, we see that the only such primes are 37, 43, 47, and 53, which gives us a total of such numbers.
Final answer
4