def convert_to_float(frac_str):
    """This function converts fractions to float, ex. -1/3 = -0.33333..."""
    try:
        return float(frac_str)
    except ValueError:
        try:
            num, denom = frac_str.split('/')
        except ValueError:
            return None
        try:
            leading, num = num.split(' ')
        except ValueError:
            return float(num) / float(denom)
        if float(leading) < 0:
            sign_mult = -1
        else:
            sign_mult = 1
        return float(leading) + sign_mult * (float(num) / float(denom))
