def boost_tpm(group_tpm, tpm, med_tpm):
    """
    Return a fraction of boost based on the expression of the IAR.

    :param float group_tpm: The TPM of the IAR.
    :param float tpm: The total boost amount allotted to this criterion.
    :param float med_tpm: The median TPM for all expressed transcripts in the patient.
    :returns: The percent of boost provided by this criterion.
    :rtype: float

    >>> boost_tpm(10, 1, 20)
    0.0
    >>> boost_tpm(10, 1, 10)
    0.35
    >>> boost_tpm(10, 1, 5)
    0.6
    >>> boost_tpm(10, 1, 2)
    0.75
    >>> boost_tpm(10, 1, 1)
    1.0
    """
    return round(tpm * ((group_tpm >= med_tpm) * 0.35 +
                        (group_tpm >= 2 * med_tpm) * 0.25 +
                        (group_tpm >= 5 * med_tpm) * 0.15 +
                        (group_tpm >= 10 * med_tpm) * 0.25), 2)