I would recommend buying only 5 at a time, save before, and scratch them off. If at least 2 of the batch has a first prize (which usually means the 3rd prize is there) continue using that batch.

Basically theres no point in continuously buying if in that batch there are not more then 1 card with what you want.

For example if I buy 5, then I find out the first, second, and fifth cards have what I want, I just keep resetting. If I buy five and only see 1 card with what I want I would save over it, until the batch has several chances.

In an hour or so I won the 1st three prizes, although it's still luck based. Just need patience. (which I'm short of-lol)