VAR
 Sum,a:Real;
 k:Integer;

BEGIN
 a:=1/2;
 Sum:=a;
 For k:=2 to 6 do
  begin
   a:=1.0/k/(k+1);
   if ((k+1) mod 2)=1 then a:=-a;
   Sum:=Sum+a;
  end;
 Writeln('Sum= ',Sum:0:5);
 Readln
END.

VAR
 P:Real;
 i:Integer;

BEGIN
 P:=1;
 For i:=2 to 8 do
  P:=P*SQR(1-1/sqr(i));
 Writeln('P= ',P:0:5);
 Readln
END.

VAR
 A:Array[1..6] of Real;
 i,N:Integer;
 M:Real;
BEGIN
 Randomize;
 M:=0;
 N:=0;
 For i:=1 to 6 do
  begin
   A[i]:=Random*100-30;
   Write(A[i]:8:2);
   If A[i]>0 then
    begin
     N:=N+1;
     M:=M+A[i];
    end;
  end;
 Writeln;
 Writeln;
 If N>0 then
  Writeln('Arithmetic mean of positive elements is ',M/N:8:2)
 else
  Writeln('There are no positive elements');
 Readln;
END.