45. Five girls are sitting on five chairs in a row, and opposite them, on five chairs, are sitting five boys. It was decided that the boys would swap places with the girls. In how many ways can this be done?
45. Boys can be seated on the girls' chairs in $5!=$ $=120$ ways. The girls can also be seated on the boys' chairs in the same number of ways. Ultimately, we will have $120 \cdot 120=14400$ ways.