Example:
$a[] = \'56\'; $a[] = \'66\'; $a[] = \'\'; $a[] = \'58\'; $a[] = \'85\'; $a[] = \'\'; $a[] = \'\'; $a[] = \'76\'; $a[] = \'\'; $a[] = \'57\';
first you need to remove empty values, otherwise average will be not accurate.
so
$a = array_filter($a); $average = array_sum($a)/count($a); echo $average;
DEMO
More concise and recommended way
$a = array_filter($a); if(count($a)) { echo $average = array_sum($a)/count($a); }
See here