There are six (6) members of the family.
The first person in the row can be any 1 of the 6. For each choice . . .
The 2nd person in the row can be any 1 of the other 5. For each choice . . .
The 3rd person in the row can be any 1 of the other 4. For each choice . . .
The 4th person in the row can be any 1 of the other 3. For each choice . . .
The 5th person in the row can be any 1 of the other 2. For each choice . . .
The 6th person in the row is the 1 who is left.
Total number of ways to line up = (6 x 5 x 4 x 3 x 2 x 1) = 720 ways .
This number is called " six factorial ", and it's written ' 6! ' .
