Invite your spectator to play a secret magical maths game. Place the 5 cards on the table and ask the spectator to select four cards. When they pick them up as them to select numbers from different cards - but they must choose different colours on all the cards. No two colours the same.
Ask them to add up the four numbers but before they do you will instantly know in seconds what the number will be... This is how....
You need to remember five number patterns and they are :
47=163, 65=145, 38=172, 31= 79, 59=151. Look at the red numbers on all the cards. Once you have remembered the number formulas then you will know the answer every time.
It is vitally important once again to make sure that the person/spectator chooses different colours from all the cards. You will know the answer by looking at the card that is left on the table and not chosen. For instance if it is the card with the number 47 in red then the outcome will be 163.
Become a magical mathematician.