Question 5
A teacher writes a two-digit prime and a one-digit prime. An and Binh calculate their sum. An’s calculator works normally; Binh’s faulty digit keys replace each entered digit d by 9−d:0→9,1→8,2→7,3→6,4→5,5→4,6→3,7→2,8→1,9→0. Both calculators display the same sum. Find the two primes.