Draw a prize with predifined chances.

gistfile1.php

$aChances = [
    0 => [
        'perc' => 25,
        'chance' => 650
    ],
    1 => [
        'perc' => 50,
        'chance' => 220
    ],
    2 => [
        'perc' => 75,
        'chance' => 25
    ],
    3 => [
        'perc' => 100,
        'chance' => 1
    ]
];

function randomDiscount( $discounts)
{
    $range = 0;
    foreach( $discounts as $discount)
    {
        $range += $discount['chance'];
        
        /* Enter the prize somewhere on the chance line */
        $prizes[ $range] = $discount['perc'];
    }
    
    $win = rand( 1, $range);
    
    foreach( $prizes as $chance => $discount)
    {
        if( $win <= $chance)
        {
            return ( $discount);
        }
    }
}

/* Benchmark */

$results = [
    25  => 0,
    50  => 0,
    75  => 0,
    100 => 0
];

//print( randomDiscount($aChances));

for ( $i = 1; $i < 40000; $i++)
{
    $results[ randomDiscount($aChances)] += 1;
}


print('<pre>');
print_r( $results);
print('</pre>');

die();