you have 16 cards,one number is printed on each card .

16 numbers on 16 cards are:

1,1,1,1,3,3,3,3 ,5,5,5,5 & 9,9,9,9

(4 cards with number 1, four with3, four with 5 and 4 with 9...)

you have to choose 6 cards such that sum of all numbers on these 6 cards will