How to select values within a provided index range from a List using LINQ

For larger lists, a separate extension method could be more appropriate for performance. I know this isn't necessary for the initial case, but the Linq (to objects) implementation relies on iterating the list, so for large lists this could be (pointlessly) expensive. A simple extension method to achieve this could be:

public static IEnumerable<TSource> IndexRange<TSource>(
    this IList<TSource> source,
    int fromIndex, 
    int toIndex)
{
    int currIndex = fromIndex;
    while (currIndex <= toIndex)
    {
        yield return source[currIndex];
        currIndex++;
    }
}

Use Skip then Take.

yourEnumerable.Skip(4).Take(3).Select( x=>x )

(from p in intList.Skip(x).Take(n) select p).sum()

You can use GetRange()

list.GetRange(index, count);