gistfile1.cs

public static class EnumerableEx
{
    public static IEnumerable<R> Select<T1, T2, R>(this IEnumerable<Tuple<T1, T2>> source, Func<T1, T2, R> f)
    {
        return source.Select(t => f(t.Item1, t.Item2));
    }
}

Enumerable.Range(1, 10)
        .Select(x => Tuple.Create(x, x))
        .Select(tuple => tuple.Item1 + tuple.Item2);
        
// F# style   
Enumerable.Range(1, 10)
        .Select(x => Tuple.Create(x, x))
        .Select((first, second) => first + second);