you would need a link script similar to this:
%CHANCE := 1D100
IF %CHANCE <= 40 THEN
$DEST := @P2
ELSE
$DEST := @P3
with CHANCE being the name of a variable
Put this code on the link of page 1:
%ROLL := 1D100
IF %ROLL <= 40 THEN
BEGIN
END
IF %ROLL > 40 THEN
It works both with items, and links, so don't you worry. xD