A: First let’s just note that the normal way to win is to take two number Keepers and essentially “graft” them together (combining the digits). Let’s call this “passive grafting” (which is no longer allowed as a way to win the game in 2.0, though you may still want the three-card bonus). If a Math Victory Rule is in play (or if you’re playing with the 2.0 deck, which has the permanent Meta Rule simply called Math Rules), you use math instead of “passive grafting” (aka “the normal way”).

The Grafting/Combine Digits Rule is meant to make it possible to create two-digit numbers for the specific purpose of subsequently using them in an equation to reach the Goal number via calculation.

For everything in Math Fluxx, you can only use numbers you can see. You can only Graft/Combine numbers you can see, and you can only use numbers you can see in an equation. Having the Grafting/Combine Digits Rule in play just lets you take two numbers-you-can-see and make them into a two-digit number-you-can-see to write out your equation.

For example, here is the equation to win Silver Jubilee (25) with Keepers One, Five, and Ten by grafting One and Five into Fifteen, and then adding it to Ten:

1 5 + 10 = 25

By contrast, here’s an illustration of how you CAN’T write out the equation to meet the Goal When I’m Sixty-Four with a One, Three, and Six by taking (1+3=4) and then grafting the resulting “4” with the Six to make 64.

6 ? (3+1) =

There is no mathematical operator that functions like “grafting” so there’s nothing you could put in place of that question-mark.