def calculate_expected_value(DataFrame, predicted_variable,
    probability_variable, ev_variable='EV'):
    """
    ev = predicted_value * probability
    
    Parameters
    ----------
    DataFrame:
    predicted_variable:
    probability_variable:
        
    Returns
    -------   
    DataFrame     
    
    """
    DataFrame[ev_variable] = DataFrame[predicted_variable] * DataFrame[
        probability_variable]
    return DataFrame
