плохо
class DoubleAB{
 public int a {get;set;}
 public int b {get;set;}
}


var obj = new DoubleAB()
obj.a = someVal * 2;
obj.b = someVal * 2;

хорошо
class DoubleAB{
 private int A = 0;
 private int B = 0;
 public int a {get {return A} ;set { A = value*2  };}
 public int b {get {return B} ;set { B = value*2  };}
}
var obj = new DoubleAB()
obj.a = someVal
obj.b = someVal