No puedo ejecutar mi php

[hamza_diaz]

Tengo un problema al ejecutar el siguiente código me dice:Notice: Undefined variable: exp in C:\Yoututs\ProbabilityDistribution\time.php on line 4

Fatal error: Call to a member function InverseCDF() on a non-object in C:\Yoututs\ProbabilityDistribution\time.php on line 4

<?php

$prob = 0.25;
$num_mins = $exp->InverseCDF($prob) * $mins_per_game;
echo "In 25 percent of games, a goal will occur within $num_mins
minutes of play.<br>";

$prob = 0.50;
$num_mins = $exp->InverseCDF($prob) * $mins_per_game;
echo "In 50 percent of games, a goal will occur within $num_mins
minutes of play.<br>";

$prob = 0.75;
$num_mins = $exp->InverseCDF($prob) * $mins_per_game;
echo "In 75 percent of games, a goal will occur within $num_mins
minutes of play.<br>";

?>

lo mismo me paso con este dice:Undefined variable: exp in C:\Yoututs\ProbabilityDistribution\time.php on line 7

Fatal error: Call to a member function CDF() on a non-object in C:\Yoututs\ProbabilityDistribution\time.php on line 7
<?php

$mins = 10;
$mins_per_game = 90;
$interval = $mins / $mins_per_game;
echo "Probability of goal in t <= 10 mins: ". $exp->CDF($interval);

?>

Por favor estare muy agradecido si alguiensabe arreglarlo