Step 1 : Let's write the inverse of the statement:
If you are not seated in rows 10 to 20, then you may not board.
Step 2: Let's write the converse of the statement:
If you may board now, you are seated in rows 10-20
Step 3: Let's write the contrapositive of the statement:
If you may not board now, then you are not seated in rows 10-20.
Hope you understand the differences between are not, may, may not and are.