I personally like to use output buffers, the third option. I gave multiple options because there’s always multiple ways to do something in PHP depending on you preferred style of coding.
Just outputting the numbers it would look something like this
if (have_rows('progress_barRepeater')) {
// start an output buffer to capture html output
ob_start()
$total = 0; // hold total from rows
$count = 0; // hold count of rows
?>
<ul>
<?php
while(have_rows) {
the_row();
$value = get_sub_field('progress_subPercent');
$total += $value;
$rows++;
?>
<li><?php echo $value</li>
<?php
} // end while have rows
?>
</ul>
<?php
// get the output buffer and store it
$html = ob_get_clean();
// calculate average
$average = $total/$count;
// display the average
echo '<p>Average = ',$average,'</p>';
// display the list
echo $html;
} // end if have rows
