Question 13233
Ooops!!  In the posted solution for this, smik seems to have missed a few of the possibilities.  


These were listed:13, 23, 30, 43, 53, 63, 73, 83, 93 .  


Also, the numbers 31, 32, 34, 35, 36, 37, 38, and 39 should have been listed.  There is a formula of sorts, there are 9 possibilities for the units digit, and 9 possibilities for the tens digit to be a 3, and then subtract one for the case in which both digits are 3, since that case was counted twice.  So there should be 9+9-1 = 17 possibilities.  Right?


R^2 at SCC