new and base

Question

Following example is provided to demonstrate Accessing Superclass Methods from a Subclass. Before new key word is use to hide the subclass method then base keyword is used to access the superclass method.

There are two questions:

-I wish to know whether it is necessary to hide superclass method every time when accessing superclass methods from a subclass.

-It seems paradox because hiding and accessing happening at the same time. If you hide how can access it.

using System;
public class BankLoan //Note: BankLoan class is created but object is not instantiated
{
private int loanNumber;
private string lastName;
protected double loanAmount;

public int GetLoanNum()
{
return loanNumber;
}
public void SetLoanNum(int num)
{
loanNumber = num;
}

public string GetName()
{
return lastName;
}
public void SetName(string name)
{
lastName = name;
}

public double GetLoanAmount()
{
return loanAmount;
}
public void SetLoanAmount(double amt)
{
loanAmount = amt;
}
}

public class DemoCarLoan2
{
public static void Main()
{
CarLoan aCarLoan = new CarLoan();
CarLoan anotherCarLoan = new CarLoan();

aCarLoan.SetLoanNum(111);
aCarLoan.SetName("Morris");
aCarLoan.SetLoanAmount(12000.00);
aCarLoan.SetYear(1992);
aCarLoan.SetMake("Toyota");

anotherCarLoan.SetLoanNum(88888);
anotherCarLoan.SetName("Jefferson");
anotherCarLoan.SetLoanAmount(18000.00);
anotherCarLoan.SetYear(2002);
anotherCarLoan.SetMake("Chevrolet");

Console.WriteLine("Loan #{0} for {1} is for {2}",
aCarLoan.GetLoanNum(), aCarLoan.GetName(), aCarLoan.GetLoanAmount().ToString("C2"));

Console.WriteLine("Loan #{0} is for a {1} {2}",
aCarLoan.GetLoanNum(), aCarLoan.GetYear(), aCarLoan.GetMake());

Console.WriteLine("Loan #{0} is for a {1} {2}",
anotherCarLoan.GetLoanNum(), anotherCarLoan.GetName(), anotherCarLoan.GetLoanAmount().ToString("C2"));

Console.WriteLine("Loan #{0} is for a {1} {2}",
anotherCarLoan.GetLoanNum(), anotherCarLoan.GetYear(), anotherCarLoan.GetMake());
}
}

class CarLoan : BankLoan
{
private int carYear;
private string carMake;

public int GetYear()
{
return carYear;
}
public void SetYear(int year)
{
carYear = year;
if (carYear < 1997)
loanAmount = 0;
}

public string GetMake()
{
return carMake;
}
public void SetMake(string make)
{
carMake = make;
}

new public void SetLoanNum(int num)
{
if (num <= 999)
base.SetLoanNum(num); // Accessing Superclass Methods from a Subclass
else
{
num = num % 1000;
base.SetLoanNum(num); // Accessing Superclass Methods from a Subclass
}
}
}
/*
Loan #111 for Morris is for $0.00
Loan #111 is for a 1992 Toyota
Loan #888 is for a Jefferson $18,000.00
Loan #888 is for a 2002 Chevrolet
*/