Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Statistical.php
public static function AVERAGE(...$args)
    {
        $returnValue = $aCount = 0;

        // Loop through arguments
        foreach (Functions::flattenArrayIndexed($args) as $k => $arg) {
            if ((is_bool($arg)) &&
                ((!Functions::isCellValue($k)) || (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_OPENOFFICE))) {
                $arg = (int) $arg;
            }
            // Is it a numeric value?
            if ((is_numeric($arg)) && (!is_string($arg))) {
                if ($returnValue === null) {
                    $returnValue = $arg;
                } else {
                    $returnValue += $arg;
                }
                ++$aCount;
            }
        }

        // Return
        if ($aCount > 0) {
            return $returnValue / $aCount;
        }

        return Functions::DIV0();
    }
public static function AVERAGE(...$args)
    {
        $returnValue = $aCount = 0;

        // Loop through arguments
        foreach (Functions::flattenArrayIndexed($args) as $k => $arg) {
            if ((is_bool($arg)) &&
                ((!Functions::isCellValue($k)) || (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_OPENOFFICE))) {
                $arg = (int) $arg;
            }
            // Is it a numeric value?
            if ((is_numeric($arg)) && (!is_string($arg))) {
                if ($returnValue === null) {
                    $returnValue = $arg;
                } else {
                    $returnValue += $arg;
                }
                ++$aCount;
            }
        }

        // Return
        if ($aCount > 0) {
            return $returnValue / $aCount;
        }

        return Functions::DIV0();
    }
AVERAGE.

Returns the average (arithmetic mean) of the arguments

Excel Function:
AVERAGE(value1[,value2[, ...]])

@category Statistical Functions

@param mixed ...$args Data values

@return float