Bài 5:
Program BTT;
Uses crt;
Var A: array[1..10000] of Longint;
i,n,t: longint;
tbc: extended;
Begin
Clrscr;
Write('Nhap so luong phan tu: '); Readln(n);
For i:=1 to n do
Begin
Write('A[',i,'] = ');
Readln(A[i]);
If (A[i]<20) or (A[i]>100) then
Begin
Write('Nhap lai A[',i,'] = ');
Readln(A[i]);
End;
End;
t:=0;
For i:=1 to n do
If A[i] mod 7 = 1 then t:=t+A[i];
tbc:=t/n;
Write('Trung binh cong la: ',tbc:0:2);
Readln;
End.