a three digit code: first number is 3 , last two numbers are odd, how many possible answers

Question

how many  possible combinations of numbers

Answer 1

311,313,315,317,319, 331, 333, 335, 337, 339, 351, 353, 357, 359, 371, 373, 375, 379, 391, 393, 395, 397, 399

 

But, really there is a permutations and combinations way to do this problem, I think.  It seems like two things taken two at a time and order does not matter...