[ServiceContract(Namespace="http://Microsoft.ServiceModel.Samples"),
XmlSerializerFormat(Style = OperationFormatStyle.Rpc, 
                                 Use = OperationFormatUse.Encoded)]
public interface IUseAndStyleCalculator
{
    [OperationContract]
    double Add(double n1, double n2);
    [OperationContract]
    double Subtract(double n1, double n2);
    [OperationContract]
    double Multiply(double n1, double n2);
    [OperationContract]
    double Divide(double n1, double n2);
}