def Likelihood(evidence, hypo):
    """Computes the likelihood of the evidence assuming the hypothesis is true.

    Args:
        evidence: the serial number of the observed train
        hypo: int hypothetical number of trains

    Returns:
        probability of seeing a given train assuming that there are N trains
    """
    train_seen = evidence
    num_trains = hypo
    if train_seen > num_trains:
        return 0.0
    else:
        return 1.0 / num_trains