Doing any type of math is for a Pick 3 game is fairly easy, since there are only 1,000 possible combinations. Sum charts have been previously published here in Lottery Post. 6 box possibilities exist for any pick which is not a double or triple, 3 box possibilities exist if the pick is a double, and only box one possibility exists if the pick is a triple.
The problem with devising a strategy in almost any Pick 3 game is the payout precentage, which doesn't change from game to game. Most jurisdictions pay out on the order of 48%-50%, with a few going as high as 60%. These percentages are unchanging, as there is no increase in payouts if the top prize is not won, as it would be in jackpot games.
Good luck.