$arr = array (75, 65, 60, 25, 4, 5);
array_splice($arr, 3, 1); // removes key[3] and thus its value (25) from array
echo '<pre>'.print_r($arr, true);
output:
Array
(
[0] => 75
[1] => 65
[2] => 60
[3] => 4
[4] => 5
)
Note that in your array, you are using [0] => 75.. but simply listing the values separated by commas has the same effect.. this is known as an indexed array.
EDIT - Seems like you are trying to create an associative array using an index structure... using the format [x] => y (associative array) would work best if you want to label your array's key names
$arr = array('soup' => 'chicken', 'bread' => 'wheat', 'cookie' => 'chocolate-chip');
echo $arr['cookie']; // output: chocolate-chip
EDIT 2- Can't believe I glossed this over.. if you were to assign say a number as a key name, it would be '0' => 75, not [0] => 75 within your array() function.