IList mixedList = new ArrayList();
mixedList.Add(0);
mixedList.Add("One");
mixedList.Add("Two");
mixedList.Add(3);
mixedList.Add(new Student() { StudentID = 1, StudentName = "Bill" });

var stringResult = from s in mixedList.OfType<string>()
                   select s;

var intResult = from s in mixedList.OfType<int>()
                select s;

var stringResult = mixedList.OfType<string>();