Place two colour arrows… one pointing left and the other right.
You deduct the highest percentage colour on a card from the other colour, and place according to the amount of remaining colour.
eg. When playing with Blue and Red Arrows:
A 20% blue / 5% Red card = is a 15% Blue Card.
A 4% Blue / 15% Red card = is an 11% Red Card.
Hardcore mode: You can take this a step further by combining two arrows pointing in one or both directions… they all tally together.
(The same colour twice in one direction signifies multiplication)
eg. When playing with Two Blue Arrows in one direction and a Red and Yellow in the other…
A 10% Blue / 5% Red / 5% Yellow card = 10% Blue. (as 10% Blue multiplied by 2 = 20% Blue, minus 5% Yellow and 5% Red = 10% Blue)