Respuesta :
					                   First row: permutation of 5 seats taken 5 (second grade students) at a time (second grade students) => 5P5
Other 4 rows: permutation of 20 seats taken 15 (first grade students) at a time => 20P15
Total different ways: 5P5 * 20P15
					                
					                
					             Other 4 rows: permutation of 20 seats taken 15 (first grade students) at a time => 20P15
Total different ways: 5P5 * 20P15
 
					                  