def get_img_dev_width_mapping(column_width):
    """
    returns a img_dev_width mapping for a given column_dev_width, e.g.
        - col-md-12 -->: 1
        - col-lg-6 -->: 1/2
    """
    wmap = {
        '1': '1/6', '2': '1/5', '3': '1/4', '4': '1/3', '5': '1/2', '6': '1/2',
        '7': '2/3', '8': '2/3', '9': '3/4', '10': '1', '11': '1', '12': '1',
    }
    k = column_width.rsplit('-', 1)[1]
    return wmap.get(k)