def boost_npa(group, npa):
    """
    Return a fraction of boost based on total number of peptides per IAR.

    :param pandas.core.frame.DataFrame group: The IAR under review.
    :param float npa: The total boost amount allotted to this criterion.
    :returns: The percent of boost provided by this criterion.
    :rtype: float

    >>> df = pandas.DataFrame({'binding_score': [0.1, 0.4, 1.5, 0.04, 0.44, \
                                                 0.1, 0.4, 1.5, 0.04, 0.44]})
    >>> boost_npa(df, 1)
    0.4
    >>> df = pandas.DataFrame({'binding_score': [0.1, 0.4, 1.5, 0.04, 0.44, \
                                                 0.1, 0.4, 1.5, 0.04, 0.44,  \
                                                 0.1, 0.4, 1.5, 0.04, 0.44, \
                                                 0.1, 0.4, 1.5, 0.04, 0.44]})
    >>> boost_npa(df, 1)
    0.9
    """
    n = len(group)
    return round(npa * ((n >= 10) * 0.4 + (n >= 15) * 0.3 + (n >= 20) * 0.2 + (n >= 30) * 0.1), 2)