1,2,3,4,5,6,7how many pairs of different numbers can be chos

1,2,3,4,5,6,7
how many pairs of different numbers can be chosen from the list above so that the sum of the two numbers is even?(note:the pair 1,3 is the same as the pair 3,1)
第二题
square tiles measuring 1/2 foot by 1/2 foot are sold in boxes containing 10 tiles each.what is the least number of the boxes of tiles needed to cover a rectangular floor that has dimensions 12 feet by 13 feet?
这道真心没看懂= =