int[] scores = { 70, 81, 62, 53, 92, 85, 77, 88, 60, 83, 100, 78, 71 };
var query = from x in scores
            group x by x / 10 into g
            select string.Format("{0}~{1}分数段的人有{2}个。"g.Key, g.Key + 10, g.Count());
foreach (string item in query)
{
    Console.WriteLine(item);
}

------解决方案--------------------
晕，修改下
C# code
int[] scores = { 70, 81, 62, 53, 92, 85, 77, 88, 60, 83, 100, 78, 71 };
var query = from x in scores
            group x by x / 10 into g
            orderby g.Key
            select string.Format("{0}~{1}分数段的人有{2}个。", g.Key * 10, g.Key * 10 + 9, g.Count());
foreach (string item in query)
{
    Console.WriteLine(item);
}