Среднее арифметическое двух любых элементов массива.

Uses crt;
 Var x:array [1..100] of integer;
      i,n,sum,k:integer;
      sr:real;
begin
clrscr;
writeln ('Vvedite kol - vo elementov  ');
Readln (n);
 for i:=1 to n do begin
    write ('Vvedite ',i, ' element ');
    Readln (x[i]);
    end;
writeln;
For i:=1 to n do
   begin
   sum:=sum+x[i];
   inc(k);
   sr:=sum/k;
   end;
Writeln ('Srednee arifmeticheskoe = ',sr:4:2);
Readln
end.

uses crt;
var a,b:integer;
    s:real;
begin
clrscr;
writeln('vvedite 1 ');
readln(a);
writeln('vvedite 2');
readln(b);
s:=0;
s:=(a+b)/2;
writeln('otvet', s:4:2);
readln;
end.

var a,b,i,c:integer;
    s:real;
    m:array[1..100] of integer;
begin
randomize;
for i:=1 to 100 do
m[i]:=random(256);
writeln('vvedite kol-vo elementov massiva');
readln(c);
for i:=1 to c do
writeln(m[i]);
writeln('vvedite nomer 1 elementa');
readln(a);
writeln('vvedite nomer 2 elementa');
readln(b);
s:=0;
s:=(m[0+a]+m[0+b])/2;
writeln('otvet ',m[0+a],'+',m[0+b],'/2','=',s:4:2);
readln;
end.

program ts3;
uses crt;
const
 n = 10;
var
 a: array[1..n] of byte;
 i: byte;
Begin
 randomize;
 for i:= 1 to n do
  a[i]:= random(50);
 writeln((a[random(n)+1]+a[random(n)+1]) div 2);
end.

program ts4;
const
 n = 10;
var
 a:array[1..n] of byte;
 i,sr:byte;
Begin
 for i:= 1 to n do
  readln(a[i]);
 write('Vvedite nomer pervogo chisla massiva : ');
 readln(i);
 sr:= sr + a[i];
 writeln;
 write('Vvedite nomer vtorogo chisla massiva : ');
 readln(i);
 writeln((sr + a[i]) div 2);
end.