Take the numbered diamond cards in a standard deck, that is those from 2 to 10. You may use some of them to form a sum: for example 23+45=68. What is the maximum result you may obtain? I hoped there was some way to obtain 10xy, but this seems not to be the case.
Two solutions in 9 cards and 1 sum:
$623+475=1098$ and $746+352=1098$
As far as I understand the rules, the maximum sum would be :
987654310 + 2 = 987654312