def boost_overlap(group_overlap, overlap):
    """
    Return a fraction of boost based on the number of overlap events in the IAR.

    :param int group_overlap: The number of overla events in the IAR.
    :param overlap: The total boost amount allotted to this criterion
    :returns: The percent of boost provided by this criterion
    :rtype: float

    >>> boost_overlap(0, 1)
    0.0
    >>> boost_overlap(1, 1)
    0.3
    >>> boost_overlap(2, 1)
    0.55
    >>> boost_overlap(3, 1)
    0.75
    >>> boost_overlap(4, 1)
    0.9
    >>> boost_overlap(5, 1)
    1.0
    """
    return round(overlap * ((group_overlap >= 1) * 0.3 +
                            (group_overlap >= 2) * 0.25 +
                            (group_overlap >= 3) * 0.20 +
                            (group_overlap >= 4) * 0.15 +
                            (group_overlap >= 5) * 0.10), 2)