procedure TForm1.Button1Click(Sender: TObject);
var
infile,outfile:textfile;
A:array[1..100] of integer;
i,n,sum:integer;
mean:single;
begin
if Opendialog1.execute then
AssignFile(infile,OpenDialog1.Filename);
reset(infile);
n:=0;
while not eof(infile) do
begin
while not eoln(infile) do
begin
n:=n+1;
read(infile,x[n]);
end;
readln(infile);
end;
CloseFile(infile);
sum:=0;
for i:=0 to n do
sum:=sum+x[i];
mean:=sum/n;
listBox1.items.add(Format(*the mean is = %f*,[mean]));
{ if Savedialog1.execute then
AssignFile(outfile,SaveDialog1.Filename);
rewrite(outfile);
writeln(outfile,mean);
Closefile(outfile);
end;
end.

这句子不难，自己挨个百度就知道了