Let the boys be A,B,C,D, and E
Choose a chair for A any one of 7 ways.
That leaves 6 seats remaining to choose for B,C,D, and E.
Choose a chair for B any one of those remaining 6 ways.
That leaves 5 chairs remaining to choose for C,D, and E.
Choose a chair for C any one of those remaining 5 ways.
That leaves 4 chairs remaining to choose for D and E.
Choose a chair for D any one of those remaining 4 ways.
That leaves 3 chairs remaining to choose for E.
Choose a chair for E any one of those remaining 3 ways.
Answer 7𡑭𠪓 = 2520 ways.
Edwin