This video shows you how to quickly unlock the platinum trophy for BlackJack Math.
You can find the gameplay, along with the text guide, below:
On Stage 1, swap the 6 and 3 cards.
On Stage 2, swap the 2 and 3 cards.
On Stage 3, swap the 8 and 5 cards.
On Stage 4, swap the 2 and 6 cards.
On Stage 5, go back to the level select screen and then select Stage 1.
Keep completing Stage 1 through Stage 4 until all trophies unlock.