Câu 1: 

uses crt;

const fi='bai1.inp'

var f1:text;

a,b:real;

begin

clrscr;

assign(f1,fi); reset(f1);

readln(f1,a,b);

writeln(a*b:4:2);

close(f1);

readln;

end.

Câu 2: 

const fi='bai2.inp'

fo='bai2.out'

var f1,f2:text;

a,b:real;

begin

assign(f1,fi); reset(f1);

assign(f2,fo); rewrite(f2);

readln(f1,a,b);

writeln(f2,a*b:4:2);

close(f1);

close(f2);

end.

Câu 3: 

const fi='bai3.inp'

fo='bai3.out'

var f1,f2:text;

a,b:array[1..100]of real;

i,n:integer;

begin

assign(f1,fi); reset(f1);

assign(f2,fo); rewrite(f2);

n:=0;

while not eof(f1) do 

  begin

n:=n+1;

readln(f1,a[n],b[n]);

end;

for i:=1 to n do  

  writeln(f2,a[i]*b[i]:4:2);

close(f1);

close(f2);

end.

#include <bits/stdc++.h>
using namespace std;
unsigned long long a[1000],i,n,uc;
//chuongtrinhcon
unsigned long long ucln(long long a,long long b)
{
    if (b==0) return(a);
    else return(ucln(b,a%b));
}
//chuongtrinhchinh
int main()
{
    freopen("sn3.inp","r",stdin);
    freopen("uc.out","w",stdout);
    cin>>n;

for (i=1; i<=n; i++) cin>>a[i];

uc=ucln(a[1],a[2]);

for (i=3; i<=n; i++)

uc=ucln(uc,a[i]);

cout<<uc;
    return 0;
}

program du_lieu;

uses crt;

var i,n:integer;

a:array[1..100]of integer;

tbc:real;

f:text;

begin

clrscr;

assign(f,'DULIEU.INP');reset(f);

readln(f,n);

for i:=1 to n do

begin

read(f,a[i]);

end;

close(f);

for i:=1 to n do

tbc:=tbc+a[i];

writeln(tbc/n);

readln;

end.

uses crt;

const fi='dulieu.txt'

var f1:text;

a,b:array[1..100]of integer;

i,n:integer;

begin

clrscr;

assign(f1,fi); reset(f1);

n:=0;

while not eof(f1) do 

begin

inc(n);

readln(f1,a[n],b[n]);

end;

for i:=1 to n do 

begin

  if a[i]<b[i] then writeln(a[i])

else writeln(b[i]);

end;

readln;

end.

uses crt;

const fi='dulieu.inp'

var f1:text;

a:array[1..100]of integer;

n,i,t1,t2:integer;

begin

clrscr;

assign(f1,fi); reset(f1);

readln(f1,n);

for i:=1 to n do 

  read(f1,a[i]);

t1:=0;

t2:=0;

for i:=1 to n do 

 begin

if a[i]>0 then t1:=t1+a[i];

if a[i]<0 then t2:=t2+a[i];

end;

writeln('Tong cac so duong la: ',t1);

writeln('Tong cac so am la: ',t2);

close(f1);

readln;

end.

const fi='tong.inp'

fo='tong.out'

var f1,f2:text;

a:array[1..100]of integer;

n,i,t:integer;

begin

assign(f1,fi); reset(f1);

assign(f2,fo); rewrite(f2);

readln(f1,n);

for i:=1 to n do 

  read(f1,a[i]);

t:=0;

for i:=1 to n do 

  t:=t+a[i];

writeln(f2,t);

close(f1);

close(f2);

end.