Random choices with weight adjustable

choices.php

<?php
// define options with chance weight
$choices = [
  'a' => 10.50,
  'b' => 30,
  'c' => 24.50,
  'd' => 35,
];

$total = array_sum( $choices ); // total chance
$percent = rand( 0, $total*100 ) / 100; // random chance with decimal point
$award = null;
$carry = 0;

// loop through each option
foreach ( $choices as $key => $value ) {
  // calculate for floor/ceil value for current option
  $high = $carry + $value;
  $low = $carry;

  // check if randomized $percent inside the threshold
  if ( $percent > $low && $percent <= $high ) {
    $award = $key;
    
    // value inside the threshold, break loop.
    break;
  }

  // value outside the threshold, save next low value and continue.
  $carry += $value;
}

// output
echo "percent: {$percent}\n";
echo "award: {$award}\n";