It takes brothers John and Dan the same amount of time each to clean the room they share but John can mow the lawn faster than Dan which action would give them a comparative advantage?

If they both shared each task equally

If john mowed the lawn and dan cleaned the room

If Dan mow the lawn and John clean the room

If Dan did both tasks

The action that would yield a comparative advantage is if John mowed the lawn and Dan cleaned the room. By doing that, they'll save time by means of division of labor. Since Dan and John perform identically in cleaning the room, the decisive part is the job one of them does faster than the other. By allocating a chore to each of them given their potential, they'll be able to perform different tasks at the same time, which would give them that advantage.

There could be a comparative advantage if both of them shared each task equally. This way the variable of cleaning can be fixed and the two can both know the output of the work that they've done and how long they could exactly finish each task.