<?php
	
	$array = array (
	  'Dit hotel' => 
	  array (
		'Sep 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-09-01',
			'maxmonth' => '2011-09-01',
			'nrcheck' => '1',
			'data' => '-',
		  ),
		),
		'Oct 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-10-01',
			'maxmonth' => '2011-10-01',
			'nrcheck' => '1',
			'data' => '-',
		  ),
		),
		'Nov 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-11-01',
			'maxmonth' => '2011-11-01',
			'nrcheck' => '1',
			'data' => '-',
		  ),
		),
		'Dec 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-12-01',
			'maxmonth' => '2011-12-01',
			'nrcheck' => '1',
			'data' => '-',
		  ),
		),
	  ),
	  'Test' => 
	  array (
		'Sep 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-09-01',
			'maxmonth' => '2011-09-01',
			'nrcheck' => '90',
			'data' => '71.5',
		  ),
		),
		'Oct 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-10-01',
			'maxmonth' => '2011-10-01',
			'nrcheck' => '90',
			'data' => '67.0',
		  ),
		),
		'Nov 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-11-01',
			'maxmonth' => '2011-11-01',
			'nrcheck' => '92',
			'data' => '63.1',
		  ),
		),
		'Dec 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-12-01',
			'maxmonth' => '2011-12-01',
			'nrcheck' => '90',
			'data' => '57.5',
		  ),
		),
	  ),
	  'MPI' => 
	  array (
		'Sep 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-09-01',
			'maxmonth' => '2011-09-01',
			'nrcheck' => '90',
			'data' => '71.5',
		  ),
		),
		'Oct 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-10-01',
			'maxmonth' => '2011-10-01',
			'nrcheck' => '90',
			'data' => '67.0',
		  ),
		),
		'Nov 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-11-01',
			'maxmonth' => '2011-11-01',
			'nrcheck' => '92',
			'data' => '63.1',
		  ),
		),
		'Dec 11' => 
		array (
		  0 => 
		  array (
			'minmonth' => '2011-12-01',
			'maxmonth' => '2011-12-01',
			'nrcheck' => '90',
			'data' => '57.5',
		  ),
		),
	  ),
	);

	foreach ($array['Dit hotel'] as $key => $value) {
	
		$array['MPI'][$key][0]['data'] = $value[0]['data'] / $array['Test'][$key][0]['data'] * 100;
	}

	var_dump($array);

?>

array(3) {
  ["Dit hotel"]=>
  array(4) {
    ["Sep 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-09-01"
        ["maxmonth"]=>
        string(10) "2011-09-01"
        ["nrcheck"]=>
        string(1) "1"
        ["data"]=>
        string(1) "-"
      }
    }
    ["Oct 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-10-01"
        ["maxmonth"]=>
        string(10) "2011-10-01"
        ["nrcheck"]=>
        string(1) "1"
        ["data"]=>
        string(1) "-"
      }
    }
    ["Nov 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-11-01"
        ["maxmonth"]=>
        string(10) "2011-11-01"
        ["nrcheck"]=>
        string(1) "1"
        ["data"]=>
        string(1) "-"
      }
    }
    ["Dec 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-12-01"
        ["maxmonth"]=>
        string(10) "2011-12-01"
        ["nrcheck"]=>
        string(1) "1"
        ["data"]=>
        string(1) "-"
      }
    }
  }
  ["Test"]=>
  array(4) {
    ["Sep 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-09-01"
        ["maxmonth"]=>
        string(10) "2011-09-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        string(4) "71.5"
      }
    }
    ["Oct 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-10-01"
        ["maxmonth"]=>
        string(10) "2011-10-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        string(4) "67.0"
      }
    }
    ["Nov 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-11-01"
        ["maxmonth"]=>
        string(10) "2011-11-01"
        ["nrcheck"]=>
        string(2) "92"
        ["data"]=>
        string(4) "63.1"
      }
    }
    ["Dec 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-12-01"
        ["maxmonth"]=>
        string(10) "2011-12-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        string(4) "57.5"
      }
    }
  }
  ["MPI"]=>
  array(4) {
    ["Sep 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-09-01"
        ["maxmonth"]=>
        string(10) "2011-09-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        float(0)
      }
    }
    ["Oct 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-10-01"
        ["maxmonth"]=>
        string(10) "2011-10-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        float(0)
      }
    }
    ["Nov 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-11-01"
        ["maxmonth"]=>
        string(10) "2011-11-01"
        ["nrcheck"]=>
        string(2) "92"
        ["data"]=>
        float(0)
      }
    }
    ["Dec 11"]=>
    array(1) {
      [0]=>
      array(4) {
        ["minmonth"]=>
        string(10) "2011-12-01"
        ["maxmonth"]=>
        string(10) "2011-12-01"
        ["nrcheck"]=>
        string(2) "90"
        ["data"]=>
        float(0)
      }
    }
  }
}