Question 1109902
.
<pre>
In all, there are 21 = 19+2 persons to be arranged in sequence.


Anyone of     21           persons can be placed in the 1-st position.

Anyone of the 20 remaining persons can be placed in the 2-nd position.

Anyone of the 19 remaining persons can be placed in the 3-rd position.


   . . . and so on . . . 


In all, there are 21! arrangements.
</pre>

Solved.