Required merit badges

The list of Required merit badges is a list of 15.
You have to do at least 12.
If you don't like to swim, you may choose bicycling or hiking and emergency preparedness.
You have to get either: Swimming, Bicycling, or Hiking.
You have to get either Lifesaving or Emergency Preparedness.
Those are the only ones that can get replaced.

If you have Swimming and Hiking, you may use them as 2 required merit badges towards a rank advancement until you are going for the Eagle, then you have to move the second one in the one area to the electives column.
If you have swimming, hiking, lifesaving, and emergency preparedness, they would count as 4 required merit badges towards the rank of Star or Life. But when you go for Eagle, since they are 4 required from 2 lists, the second one earned of each "list" has to be counted as an elective.