Andy writes down the largest two-digit prime such that each of its digits is prime.  Baker writes down the smallest three-digit prime such that each of its digits is prime.  Carl adds Andy\textquotesingle s number and Baker\textquotesingle s number.  What answer does Carl obtain? ． 
Overseas Competition->Knowledge Point->Number Theory Modules->Prime and Composite Numbers->Applying Special Prime Numbers
The prime digits are $$2$$, $$3$$, $$5$$ and $$7$$. So the largest two-digit integer whose digits are both prime is $$77$$. However, $$77$$ is not prime, nor is $$75$$, but $$73$$ is prime. So Andy writes down $$73$$. The smallest three-digit integer whose digits are both prime is $$222$$. However, $$222$$ is not prime, but $$223$$ is prime.  So Baker writes down $$223$$. Therefore the answer which Carl obtains is $$73 +223 = 296$$. 