How to sum up values from specific dropdown only

Question

I have a dropdown as shown below. I need to sum up the values of all the dropdowns that have a specific name as indicated.

jQuery(function () {
    $('select').change(function(){
        var sum = 0;
        $('select :selected').each(function() {
            sum += Number($(this).val());
        });
         $("#sum").html(sum);
    });
});

<h6>Nunber <a id="sum">0</a></h6>

<div class="form-group mb-2">
    <label>Select Repetition</label> <br>
    <select id="ddlViewBy"  name="repetition[]" >
       <option value="1">1</option>
       <option value="2">2</option>
       <option value="3">3</option>
       <option value="4">4</option>
       <option value="5">5</option>
    </select>
</div>

Using the code below, I am able to duplicate the dropdown above into as many dropdowns as I need.

<script> 
    $(document).ready(function(){
        $(document).on('click', '.remove-btn', function() {
            $(this).closest('.main-form').remove();
        });
        $(document).on("click", ".add-more-form", function() {
            $('.paste-new-forms').append('
                <label>Select Repetition</label> <br>\
                <select id="ddlViewBy" name="repetition[]">\
                    <option value="1">1</option>\
                    <option value="2">2</option>\
                    <option value="3">3</option>\
                    <option value="4">4</option>\
                    <option value="5">5</option>\
                </select>\
                <button onClick="onUnClick()" type="button" class="btn-danger">X</button>\
            ');
        });
    });
</script>

Problem: The code appears to sum everything including values from other dropdowns in my form. I am interested in the dropdowns with the name repetition[] only.