Decided to give Mark Heath's lunchtime LINQ challenge a go. http://mark-dot-net.blogspot.co.uk/2013/06/lunchtime-linq-challenge.html

challenge1.cs

var data = "Davis, Clyne, Fonte, Hooiveld, Shaw, Davis, Schneiderlin, Cork, Lallana, Rodriguez, Lambert";
var result = data.Split(',').Select((str, index) => String.Format("{0}. {1}", index+1, str.Trim()));

challenge2.cs

string data = "Jason Puncheon, 26/06/1986; Jos Hooiveld, 22/04/1983; Kelvin Davis, 29/09/1976; Luke Shaw, 12/07/1995; Gaston Ramirez, 02/12/1990; Adam Lallana, 10/05/1988";

var results = from i in data.Split(';')
              let split = i.Split(',')
              let timeDiff = DateTime.Now - DateTime.Parse(split[1].Trim(), new CultureInfo("en-GB"))
              let age = DateTime.Now.Year - DateTime.Parse(split[1].Trim(), new CultureInfo("en-GB")).Year
              orderby timeDiff
              select String.Format("{0} {1}", split[0].Trim(), age);

challenge3.cs

var data = "4:12,2:43,3:51,4:29,3:24,3:14,4:46,3:25,4:52,3:27";

var timeTotal = (from a in data.Split(',')
                 select TimeSpan.Parse("0:" + a)).Sum(x => x.TotalSeconds);

challenge4.cs

var points = from i in Enumerable.Range(0, 3)
             from j in Enumerable.Range(0, 3)
             select String.Format("{0}, {1}", i, j);

challenge5

var data = "00:45,01:32,02:18,03:01,03:44,04:31,05:19,06:01,06:47,07:35".Split(',');

var results =
          data.Select(x => new TimeSpan(0, int.Parse(x.Split(':')[0]), int.Parse(x.Split(':')[1])))
              .Select(
                  (current, index) =>
                  String.Format("{0}", current - (index > 0 ? TimeSpan.Parse("0:" + data[index - 1]) : new TimeSpan())));

challenge6.cs

var data = "2,5,7-10,11,17-18";
var results = data.Split(',').SelectMany(x => Regex.IsMatch(x, @"\d-\d")
                                    ? (Enumerable.Range(int.Parse(x.Split('-')[0]),
                                                        int.Parse(x.Split('-')[1]) -
                                                        int.Parse(x.Split('-')[0]) + 1))
                                    : new[] {int.Parse(x)});