Any two numbers that you choose can match a number from his.
There are 15 different sums that you can get: 1/2 1/3 1/4 1/5 1/6 2/3 2/4 2/5 2/6 3/4 3/5 3/6 4/5 4/6 5/6
Each of these sums can be chosen in two ways, so there are a possible 30 different selections for you.
If Mathew chooses first, then any number that he chooses (provided that his choice is larger than 2 and smaller than 12
can be matched by the choices listed above.