Depend on Behaviour not data: Here we make the change only once, but it is reflected everywhere. It's much easier to maintain.

DependOnBehaviourNotData-p3.md

/// Notice how similar it is to the first example? 
/// The code is only changed in one place
/// and the change is propogated everywhere else

    class Program
    {
        static void Main(string[] args)
        {
            Account freddie = new Account(5000000);

            // freddie buys a grand piano
            freddie.balance = freddie.balance - 500000m;

            // freddie buys a leather jacket
            freddie.balance = freddie.balance - 5000m;

            // freddie buys a beer in Singapore
            freddie.balance = freddie.balance - 20;            
        }                
    }


    public class Account
    {
        private decimal _balance;

        public decimal balance
        {
            get
            {
                _balance = _balance * 1.25m;
                return _balance;
            }
            set { _balance = value; }
        }

        public Account(decimal balance)
        {
            this._balance = balance;
        }
    }