If a ratio of skiers and snumboarders is 1:2, and if there are 1250 snowboarders more than skiers, it means that is that there 2500 snowboarders and 1250 skiers.
How to check it? 2500 is 1250 more than 1250 and the ratio is still 1:2 (there are two times more snowboarders than skiers). Both conditions are fulfiled, so it's correct.
