Find the bond
Put Numicon pieces 1 to 10 in a row. Put another set of pieces 1 to 10 in a bag. Take turns to pick a Numicon from the bag and take the piece from the row that would bond with it to make 10. Check by putting both pieces together and comparing them with a 10. If you chose the correct piece, you may keep both, otherwise return them to the bag and the row. The winner is the one with most pieces.
On your turn, choose a Numicon from the row first, then feel in the bag to find its bond for 10.
Play as the initial game, but put 2 sets of Numicon pieces 1 to 10 in the bag. As you play, you will have to feel carefully to find a Numicon that still has its bond left in the row!
You could also play this game with Cuisenaire rods or wooden/plastic numbers instead of Numicon.