How many 4-digit numbers are there in 123456
First, choose any four numbers in 123456, there are 15 kinds. Each kind of four numbers has 24 kinds of arrangement, there are 24 different four digits. Finally, public 15 * 24 = 360
First, choose any four numbers in 123456, there are 15 kinds. Each kind of four numbers has 24 kinds of arrangement, there are 24 different four digits. Finally, public 15 * 24 = 360