For Jo, pair the numbers together: 1+49 = 50, 2+48 = 50, ..., 24+26 = 50. Then add the two remaining numbers: 25+50.
For Kate, 1,2,3, and 4 all round down to 0. 5 through 14 all round to 10 (there are 10 such values). 15 through 24 all round to 20 (another 10 values). 25 through 34 round to 30, 35 through 44 round to 40, and 45 to 50 round to 50 (only six values for this last group of numbers).